There is nothing that Microsoft can do to help your friend.
Let's say that someone steals your wallet - I hope that never happens to you. Within the first few minutes of having your wallet in their possession, the thief will take out all the cash, all your cards, and all your identifying information, and then abandon your wallet. Because they don't need it any more - they already have everything about you that they need.
Now let's say you fill out all kinds of online forms and respond to all kinds of robotic prompts, and the end result is that you have your wallet in your possession once again. Does that mean you are safe? Of course not. You won't get back the cash the thief took, but even more important: the attacker has all your information and can you use it just as if they were you.
A Microsoft account is like a digital wallet. When someone steals your Microsoft account, within the first few minutes of having it in their possession, they will copy all the information about you that they need.
Let's say you fill out all kinds of online forms and respond to all kinds of robotic prompts, and the end result is that you regain possession of your Microsoft account. Does that mean you are safe? Of course not. The thief still has all your information.
This is why Microsoft can't help your friend. Even if they could, it wouldn't make any difference.
Your friend can't afford to waste time. What they have to do now is to disconnect themselves from their former account as much as they possibly can, and then start over.