okay so delete your 1.12 mw2 patch then download elite mossy patch blocker and go onto your system and use the proxy and then type the numbers from the patch blocker in there, Now dont "hit blocking" until after you finish setting up your connection. So finish the connection (dont test it). Now start blocking!
After you start blocking, run mw2 and goto multiplayer then online, it will say you must be signed in order to play online, Sign in, and it should work