X Box Account Hacked and cant get it resolved with Microsoft

My grandsons Xbox account was hacked and my daughter has been going back and forth furnishing info to Microsoft and nothing is getting resolved. There were pages and pages of purchases and it came up to over $700 which my daughter has not been refunded. Microsoft keeps saying they need more info and when she sends it they want more. Now they are saying its too late. This is not right, Microsoft initially said they could see it was hacked and I think they said in London but she needs that money. It is even harder when it all has to be done through email and they don't have a phone number. What do they do?

:)