tcp socket, cannot bind to port - in use

Ive got a c++ program that acts as a server (sends/receives). I'm trying to connect to the port that the server is using (say 2222). However, the message I'm getting is that the port is already bound to. The port is in use. I'm wondering how can I connect to this open port (bearing in mind the c++ tcp program is closed source)? I can change the source of the c++ program if needed, but it seems strange that I cannot just connect to the port it's using. I wonder do I need to implement threading in the tcp program, so that the send and receive's are using a different port?