Please note that this is a community forum and we do not have access to any account data or information.
If his email address was changed by the hacker, I suggest you fill out this form https://aka.ms/recovermyaccount, which will be sent to a team specially to handle this type of issue.
Use this guide to help you complete it;
https://support.microsoft.com/account-billing/guidance-notes-for-the-microsoft-account-recovery-form-4dd8fef1-33d2-4fbe-9352-66127ab9b50e
You should receive a response via email. It may take up to 72 hours. If you don't receive a response after this time, please check your spam folder.