Daughters account was hacked and email changed

My daughters Xbox account was hacked and the email for her Gamertag was changed. Now when I go to login to Microsoft with the email used for her account it says that the email does not exist. I can't get anybody from Microsoft to call me back because of this issue and I am having a hell of a time getting this resolved... I have spent A LOT of money on games, movies, DLC, etc over the past 15 years between my Xbox account and now my kids. I don't want to lose everything that I have paid for on her Account. Is there anything I can do? I have the email that the hacker uses for her account now, I have her Email that was used along with her Gamertag, Bank statements for her xbox account, and basically everything I would need to prove that the account was hacked and stolen... Please help me out here, I am sick to my stomach that somebody would do this to a child and she feels even worse to the point where she can't eat because she is scared she won't get her account back.

:)