You say, you are getting response from web- service. That means it is working fine. I think there is some problem sending post parameters from url to the web-service.
Try something like this(just a piece of code. you need to modify it accordingly):
NSString * parameters = [NSString stringWithFormat:@"email=%@&password=%@",self.txtUserEmail.text,self.txtUserPassword.text];
[_mutableRequest setHTTPMethod:@"POST"];
NSData *requestData = [NSData dataWithBytes:[parameters UTF8String] length:[parameters length]];
[_mutableRequest setHTTPBody:requestData];
// then hit the connection using NSURLConnection