What to do about fake Xbox live account?

My little brother - aged 7 - decided it would be a good idea to make a fake Xbox live account. He used a fake name and address but he will not tell me / "he can't remember" if he put in fake card details or anything to pay it with. From what I can see he hasn't but there's a payment option and I'm scared he ll use a fake one which will end up being someone's real one. I know I'm not making a lot of sense. The account info says it's free but I'm not certain. I went to delete the account but he says it has all his work on it, and I d feel bad deleting it. Plus I have a minecraft world on that account. What should I do? Should I delete it and make him hate me or can I deactivate only the Xbox live account and leave the Xbox account with the data on it?

Xbox has many ways to view and check the authenticity of credit card credentials. Though, if it miraculously turns out to actually be someone's account, then he/your parents could get into a lot of trouble. He can sign in with another account and transfer all of his game data to there.

https://support.xbox.com/...games-data