What console are you playing on? Also, try and check your in game connectivity info for your game. To check for it, go to multiplayer, connect online/xbox live then go to options. Check at the bottom part of your screen to see if what button you should press ("select" for PS3, "back" button for X360, "S" for PC). This may be due to matchmaking...
A support case was created for you and you should be contacted shortly by a Customer Support Representative, if you haven't been already. You can view and update your case at the Activision Support website. After logging in, go to "My Support" then "My Cases".