What to do if hacked?

I suggest contacting support and explaining situation

If you have decent to good evidence of having been hacked, try and contact a Microsoft representative (most likely through support) and they will have to personally help to see what can be done next. After that, you should probably change your Microsoft
Account password, add extra security to the account available through http://account.microsoft.com , and then make sure nothing in your bank account has been changed or charged.

There's a "compromised account" solution page here https://support.xbox.com/en-US/my-account/security/compromised-account-solution

Make sure you change your password and update any security and password recovery information if you haven't already done so.

You have to contact customer support for this and talk to them about this issue and you can give them evidence of his hacks to get him banned

You can use his IP address too trace his xbox account and report him too get him banned.