Консольное приложение для анализа html, подсчета тегов img и отправки данных формы в C #

Question

Я создал консольное приложение на C #, которое будет загружать html-контент с сайта, анализировать html-содержимое, чтобы получить счетчик тега img на основе src, и опубликовать данные формы обратно. Когда я делаю это, сервер отвечает неправильным ответом. Я не понимаю, что может пойти не так. Я считаю тэг img вручную, отображая содержание html и совпадения ответов. Мне было интересно, если он должен иметь все заголовки по запросу? Не могли бы вы, эксперты, помочь мне разобраться в этом.

    using HtmlAgilityPack;
    using System;
    using System.Collections.Generic;
    using System.IO;
    using System.Linq;
    using System.Net;
    using System.Net.Http;
    using System.Text;
    using System.Threading.Tasks;

    namespace ConsoleApplication1 {
        public class Program {
            public static void Main(string[] args) {
                var client = new WebClient();
                var html = client.DownloadString("//URI- comes- here");
                Console.WriteLine(html);

                var htmlDoc = new HtmlDocument();
                htmlDoc.LoadHtml(html);

                int count = htmlDoc.DocumentNode.SelectNodes("//img[@src='filledO.gif']").Count;
                Console.WriteLine(count);

                string postData = String.Format("title={0}&jobref={1}&valuee={2}", "submit", "P0162", count);

                client.Headers.Add("Content-Type", "application/x-www-form-urlencoded");
                client.Headers.Add(HttpRequestHeader.Cookie, "PHPSESSID=dl1il0k58qb6ebn08bsv7nns36;");
                client.Headers.Add("User-Agent", "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/74.0.3729.131 Safari/537.36");
                client.Headers.Add("Accept", "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3");
                client.Headers.Add("Accept-Language", "en-US,en;q=0.9");

                // Upload the input string using the HTTP 1.0 POST method.
                byte[] byteArray = System.Text.Encoding.ASCII.GetBytes(postData);
                byte[] byteResult = client.UploadData("//URI- comes- here", "POST", byteArray);
                // Decode and display the result.
                Console.WriteLine("\nResult received was {0}", Encoding.ASCII.GetString(byteResult));

                //PostContent("//URI- comes- here", count); // calling the function to post the form data to the dataprocessors server
            }

            private static void PostContent(string urlAddr, int filledCircleCount) {
                HttpWebRequest request = (HttpWebRequest) WebRequest.Create(urlAddr);
                var postData = "title=submit";
                postData += "&ref=P0162";
                postData += "&valuee=" + filledCircleCount;

                var data = Encoding.ASCII.GetBytes(postData);

                request.Method = WebRequestMethods.Http.Post;
                request.ContentType = "application/x-www-form-urlencoded";
                request.ContentLength = data.Length;
                request.Headers["Cookie"] = "_ga=GA1.3.1376683341.1556868600; PHPSESSID=dl1il0k58qb6ebn08bsv7nns36; pc3o=d2r22";
                request.UserAgent = "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/74.0.3729.131 Safari/537.36";
                request.Accept = "*/*";
                request.Referer = "uri comes here";

                using(Stream stream = request.GetRequestStream()) {
                    stream.Write(data, 0, data.Length);
                }

                HttpWebResponse response = (HttpWebResponse) request.GetResponse();

                var responseString = new StreamReader(response.GetResponseStream()).ReadToEnd();
                Console.WriteLine(responseString);
                response.Close();
            }
        }
    }

**The Html that I get is**
   HTTP/1.1 200 OK
   Date: Fri, 10 May 2019 11:00:42 GMT
   Server: Apache/2.4.10 (Amazon) PHP/5.5.17
   X-Powered-By: PHP/5.5.17
   Expires: Thu, 19 Nov 1981 08:52:00 GMT
   Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0
   Pragma: no-cache
   Content-Length: 6229
   Keep-Alive: timeout=5, max=100
   Connection: Keep-Alive
   Content-Type: text/html; charset=utf-8

  <html>
   <head>
    <title>Answer the question</title>
  </head>
   <body>
     <h1>Solve the puzzle</h1>
      <form action="" method="POST">
        <input type="hidden" name="title" value="submit">
      <p>Ref No: <input type="text" name="ref" value="" size="10"></p><p>How 
many filled circles do you see:? <br><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="filledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="filledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><br><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="filledO.gif" height="12" width="12"><img src="filledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><br><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="filledO.gif" height="12" width="12"><img src="filledO.gif" height="12" width="12"><img src="filledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="filledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><br><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="filledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="filledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="filledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="filledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="filledO.gif" height="12" width="12"><img src="filledO.gif" height="12" width="12"><br><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="filledO.gif" height="12" width="12"><img src="filledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="filledO.gif" height="12" width="12"><img src="filledO.gif" height="12" width="12"><img src="filledO.gif" height="12" width="12"><img src="filledO.gif" height="12" width="12"><img src="filledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><br><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="filledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="filledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="filledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="filledO.gif" height="12" width="12"><img src="unfilledO.gif" height="12" width="12"><img src="filledO.gif" height="12" width="12"><br></p>
      <p>Answer: <input type="text" name="valuee" value="" size="10"></p>
      <p><input type="Submit" value="Submit">
    </form></body>
  </html>

The response expected is
Congratulations ....... blah blah blah 

whereas I get is 

HTTP/1.1 200 OK
Date: Fri, 10 May 2019 10:42:51 GMT
Server: Apache/2.4.10 (Amazon) PHP/5.5.17
X-Powered-By: PHP/5.5.17
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0
Pragma: no-cache
Content-Length: 168
Content-Type: text/html; charset=utf-8

  <html>
  <head>
    <title>Answer the question</title>
  </head>
  <body>
  <h1>Puzzle</h1><p>Sorry wrong answer</p></body>
  </html>