I have no indication of me being banned. The only thing I could think of is because I have secret cars… But wouldn’t the game tell me if I was banned?
“Secret cars”? And they’ve been Gifted to you? That could be the problem, especially if they’re hacked vehicles. Write the developers at forzafb@microsoft.com, giving them the full details of the cars and the gamertag of the person sending them to you.