Ok so my friend was banned for gamemarketplace theft so he called Microsoft and told them that he was accidently banned. so he told them his gamertag and they said he was on a list for people who were accidently banned and they gave him 1600 Microsoft points, a 3 month and unbanned his account. So if your banned go check with Microsoft to see if your on the list. Chances are if you did do gamemarketplace theft or any other modding you are not on the list but it is worth a shot.