so i haven’t played forza 4 in forever and i came back about a week ago to re-live the experience of possibly the best game in the world only to find that i cannot use the auction house and cannot play online? 
so i simply would like to know why i was banned as i don’t recall doing anything against the terms and conditions or making the game unfair by modding/hacking/glitching? if anyone can help i would appreciate it. such a shame that a great game (that has almost died) cannot be re-lived.
You should send the details to Turn 10 at forzafb@microsoft.com. Make sure you list all gamertags which have been used on your console, too. They will need to investigate, perhaps even assign a tech with server rights to check things before you receive a response.
Have patience, and wait for the answer.