All you have to do is say on live chat is :

1.Could you help me unlink my gamertag from my account? If they say No end chat.

2.They should then ask what your gamertag and email is. If they say they cant make changes because you are banned, end chat.

3.Then they should ask what your date of birth for the account was if you dont know they may ask you for online pass. If you dont know either end chat

4.They should then ask what you want done with the account, removed or linked to a new email. Say you want it linked to a new email, you may need to make one

5.After they have done it try play fifa and if you are unbanned then tell them if not tell them its not working
(DO not mention that it says you are banned) they should then do some stuff (not a clue) and ask you to try it again, turn your xbox on and off

Eventually they will get it to work especially if they are a sound guy!

Good Luck took me 3 or 4 tries, dont give up you will eventually get lucky.