X box Fortnite account

Hello my son deleted his Fortnite account on xbox as he was trying to access his account and couldn't get in so deleted account. The email address that was attached to the account we do not have access to. He has tried to set up a new account on the xbox but it won't allow him to as he doesn't have access to that email address. We have owned this xbox since day 1. Is there any way you are able to help us. He can access it on his Nintendo and his pc but not on the xbox. Email address that keeps popping up on x box device with passcode is not ours. Any ideas what we can do? We factory reset the xbox thinking this might help. But no it didn't. Thank you.

:)