send web request from desktop application

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C#

I need to connect to a website and send it some parameters

I searched for it for a while and found articles about the http web request object and tried it but it didn't work

the last code i reached was:

Uri uri = new Uri("https://www.hanjin.com/hanjin/CUP_HOM_3321.do?redir=Y&sessLocale=en");
string PostData = "bkgNo=" + txt_BOL.Text;
string proxy = null;
UTF8Encoding encoding = new UTF8Encoding();
byte[] bytes = encoding.GetBytes(PostData);
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(uri);
request.CookieContainer = new CookieContainer();
request.Method = "POST";
request.AllowWriteStreamBuffering = true;
request.AuthenticationLevel = System.Net.Security.AuthenticationLevel.MutualAuthRequested;
request.Credentials = CredentialCache.DefaultCredentials;
request.UseDefaultCredentials = true;
request.ProtocolVersion = HttpVersion.Version10;
request.AllowAutoRedirect = true;
request.KeepAlive = true;
request.ContentLength = bytes.Length;
request.ContentType = "text/html;charset=UTF-8";
request.Proxy = new System.Net.WebProxy(proxy, true);
request.Accept = "*/*";
System.IO.Stream dataStream = request.GetRequestStream();
dataStream.Write(bytes, 0, bytes.Length);
dataStream.Flush();
dataStream.Close();
System.Net.HttpWebResponse response = (System.Net.HttpWebResponse)request.GetResponse();
long y = response.ContentLength;
string str = response.ContentType.ToString();
System.IO.Stream resst = response.GetResponseStream(); // display HTTP response
System.IO.StreamReader sr = new System.IO.StreamReader(resst);
string result = sr.ReadToEnd();
sr.Close();
resst.Close();
response.Close();

but it never worked

and the reponse content length always is -1

can any one tell me what (respomse content length = -1) means ??
and why the code doesn't work please ??

thank you for your help