How make soap request using C#

Hello,

I am tried do query to web service. To content I am put next one:

strSoapEnvelope = "";
strSoapEnvelope += ";
strSoapEnvelope += "xmlns:xsi = \"http://schemas.xmlsoap.org/wsdl/\" ";
strSoapEnvelope += "xmlns:xsd= \"http://www.w3.org/2001/XMLSchema\" ";
strSoapEnvelope += "xmlns:soap= \"http://schemas.xmlsoap.org/wsdl/soap/\">";
strSoapEnvelope += "";
strSoapEnvelope += "";
strSoapEnvelope += "string_1";
strSoapEnvelope += "string_2";
strSoapEnvelope += "";
strSoapEnvelope += "";
strSoapEnvelope += "";
strSoapEnvelope += "";
strSoapEnvelope += "";
strSoapEnvelope += "";
strSoapEnvelope += "";
strSoapEnvelope += "";
strSoapEnvelope += "";
strSoapEnvelope += "";
strSoapEnvelope += "";
strSoapEnvelope += "";
strSoapEnvelope += "";

And response is:

http://schemas.xmlsoap.org/soap/envelope/" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:SOAP-ENC="http://schemas.xmlsoap.org/soap/encoding/">SOAP-ENV:ServerInvalid SOAP request


First I tried do Web reference, I got all functions and parameters to use. When I made this method I got error: Cannot convert System.bool to System.String.
This function return boolean value, string value and someStruct struct.