Unrecoverable Hotmail

I, as a parent, changed the password on my son's account some time ago but now can't remember it.  He doesn't really use his hotmail.  It is just the default address for his Facebook. A reset can't be sent to his phone as his old phone that it was attached to no longer exists.  Neither of us has used his account for a very long time and, as such, can't answer adequate recovery questions to have the password reset send to a different email.  His Facebook defaults to this one hotmail account, which won't do him any good if we can't get access to it.  What do we do to recover a password?  Too many attempts at guessing locks us out of course.