There is often very little can be done to recover an account when a hacker has changed the details.
There are recovery forms :
https://account.live.com/password/reset but it's unlikely to resolve the problem.
You can try the Get Help app or https://support.microsoft.com/en-us/contactus/ but you will need to create a new account for the best results. The type chat with an agent and select Contact Support.
Another user found this method help them:
from what i experience Microsoft’s support flow often redirects into loops, which can be frustrating.
Here’s how you can bypass that and reach a real agent:
1.Go to Microsoft Support – Contact Us.
2.Scroll down and select Get Help → Contact Support.
3.When prompted to sign in, choose I can’t sign in or Skip sign-in.
4.Select Microsoft Account as the product.
5.Under Need more help?, choose Chat with a support agent or Request a call back.