Your not banned!!! I've got this problem too yesterday because my xp messed up. there's out trainer what fix that problem, you can download it on mw3 hacks section, the trainer called Modern Warfare 3: JabUnlocker V1.1 (Fixed) by jabbathehutt. There's one option called "Fix Double XP" and after that you should be okay and ur game is playable again. KTHXBYE.