I have been banned.

To add a little more, non of us have access to your account. Forums can't help other than point you in the directions we have done.

It is possible you have a suspension from Xbox Live, which is where Njal's advice would work. If you can play other games, but NOT Forza Horizon 4, you may have been banned from just that game. The forums at
Forza Motorsport will be your best place to look after that.

You will need to login at https://enforcement.xbox.com

You'll not find anyone in the forums that can lift a Suspension. You'll need to go onto the
enforcement website and submit a

Case Review if you're able to do so.

If you're able to post on this forum with the account that you believe to be banned, then you've not been banned.

Sounds like your account has been suspended due to a billing violation. You'll need to do one of two things: Update your existing payment instrument so payment for whatever is in decline can be resolved, or add a new payment instrument to your account and
the outstanding balance will be automatically transferred over on the the next cycle.