XML : WCF Webservice always returning null

I am consuming a SOAP webservice from our ticket system OTRS. So the Webservice is not really under my control. The request works just fine, but i am never getting an answer in my Code. The answer is always null. (var response = client.SessionCreate(session);) The strange thing is, that wireshark and the webservice console of that ticket system are saying that i should receive a valid answer. Since i am very new to this webservice stuff so i have absolutely no idea where to start in this case. So here is a description of that i did. Any suggestion is really appreciated.

First i created a normal C# project and added the WSDL file which can be found only on the GitHub site website of the OTRS project. I added it as a Service Reference and than added my C# code which looks like this.

// For Debug System.Net.ServicePointManager.Expect100Continue = false; Thread.CurrentThread.CurrentUICulture = new CultureInfo("en-us");

  try  {      OTRS.OTRS_Error err = new OTRS.OTRS_Error();      OTRS.GenericTicketConnector_PortTypeClient client = new OTRS.GenericTicketConnector_PortTypeClient("GenericTicketConnector_Port");        OTRS.SessionCreate session = new OTRS.SessionCreate();      session.Item = "someUserNameGoesHere";      session.ItemElementName = OTRS.ItemChoiceType8.UserLogin;      session.Password = "SomePasswordGoesHere";        var response = client.SessionCreate(session);        Console.WriteLine(response.SessionID);      Console.WriteLine(response.Error);  }  catch (Exception exep)   {      Console.WriteLine(exep.Message);      Console.WriteLine(exep.InnerException);  }  finally   {      Console.ReadLine();  }    

Incoming message at serverside

  <s:Envelope xmlns:s="http://www.w3.org/2003/05/soap-envelope" xmlns:a="http://www.w3.org/2005/08/addressing">  <s:Header>      <a:Action s:mustUnderstand="1">http://www.otrs.org/TicketConnector/SessionCreate</a:Action>      <a:MessageID>urn:uuid:14750529-3de2-4618-8db4-8ac18b681c18</a:MessageID>      <a:ReplyTo>          <a:Address>http://www.w3.org/2005/08/addressing/anonymous</a:Address>      </a:ReplyTo>      <a:To s:mustUnderstand="1">http://SomeServer/otrs/nph-genericinterface.pl/Webservice/GenericTicketConnector</a:To>  </s:Header>  <s:Body xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">      <SessionCreate xmlns="http://www.otrs.org/TicketConnector/">          <UserLogin xmlns="">someUserName</UserLogin>          <Password xmlns="">somePassword</Password>      </SessionCreate>  </s:Body>    

Outgoing message at serverside

  <?xml version="1.0" encoding="UTF-8"?>  <soap:Envelope soap:encodingStyle="http://www.w3.org/2003/05/soap-encoding"   xmlns:soap="http://www.w3.org/2003/05/soap-envelope"   xmlns:soapenc="http://www.w3.org/2003/05/soap-encoding"   xmlns:xsd="http://www.w3.org/2001/XMLSchema"   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">      <soap:Body>          <SessionCreateResponse xmlns="http://www.otrs.org/TicketConnector/">              <SessionID>SomeSessionID</SessionID>          </SessionCreateResponse>      </soap:Body>  </soap:Envelope>    

Wireshark HTTP/XML package going from the server to my client

  <?xml version="1.0" encoding="UTF-8"?>  <soap:Envelope soap:encodingStyle="http://www.w3.org/2003/05/soap-encoding"   xmlns:soap="http://www.w3.org/2003/05/soap-envelope"   xmlns:soapenc="http://www.w3.org/2003/05/soap-encoding"   xmlns:xsd="http://www.w3.org/2001/XMLSchema"   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">      <soap:Body>          <SessionCreateResponse xmlns="http://www.otrs.org/TicketConnector/">              <SessionID>SomeSessionID</SessionID>          </SessionCreateResponse>      </soap:Body>  </soap:Envelope>    

Refernce.cs https://gist.github.com/HansVader/1ba3847d918ee15ef16703c8ada6c9bf

WSDL https://gist.github.com/HansVader/dd849e49f4a1584397cd21b0e430b301

I currently only need the SessionnCreate and TicketUpdate function. The other operations are irrelevant at this point in time. Please let me know if you need any other informations.