Managing personal Outlook.com account settings, security, and privacy
Before you do anything else, do this first:
Think of all the personal information you may have in your Microsoft account - credit cards, Paypal, email contacts, passwords, personal information stored in OneDrive, among other things. Your attacker has all that in their possession now. And they will continue to have it in their possession even if you can retrieve your account, because unless your attacker is a complete amateur they copied all that information within the first few minutes of stealing your account.
Now think of all the damage they can do to your reputation, your credit score and your finances with all that information.
Now think of all the bad things the attacker can do with your Microsoft account - I'll remind you: they can send spam in your name, they can commit crimes in your name, and they can attack other computers in your name.
Before you do anything else, protect your identity.
If the attacker changed all the security information in your account, you will never get that account back, but you don't have to take my word on that. Once you've done everything you possibly can to protect your identity, then go ahead and chat with the bots and fill out the forms and wait for something to happen.
Protect your identity first!