Hello Kevin McDonald,
Welcome to Microsoft Q&A forum. It's my pleasure to help you today.
It's very unfortunate to hear that your son's account has been hacked, and I'm very sorry for the experience you have. I see that the hacker might have already changed the security email and your son can no longer access it.
This is a public forum, so unfortunately, moderators are unable to access or take action on any account for security reasons. However, you can try to contact live chat support for any issues regarding your account, please ask your son to prepare all information that he can use to prove his ownership of the account. Thank you for your understanding.
If you have any questions. Please let us know.