someone hacked my microsoft account and changed everything

Please note that this is Italian Q&A Forum, any threads should be posted in Italian. However, I will still provide an answer on English based on your initial response. 

Hello Enrico Cintioli, welcome to Microsoft Q&A.

I’m sorry to hear you’re going through this. Unfortunately, no one here on the forum (and not even Microsoft Support agents) can grant direct access to an account or change recovery details for you. The only way back in is through the official self-service recovery form: https://account.live.com/acsr 

Detailed steps on how to use the Account Recovery Form can be found here: Help with the Microsoft account recovery form 

Please note that even if you contact Microsoft Support, they will not be able to grant you access to your account, you will be sent back to the Account Recovery page. Microsoft takes account security very seriously, that's why Account Recovery is an automated process with no human influence. 

The form requires adequate information to prove that you are the owner of the account. It can be a time-consuming process, but providing as much info as possible from the start of the process will increase the possibility of being verified by the automated process. You'll need to keep trying until you're verified by Microsoft. 

Remember to use a familiar device from which you've frequently accessed your Microsoft account, as well as a familiar location. Microsoft will review your responses and respond within 24 hours. If you are verified, instructions on how to log back into your account will be sent to you, and if you are not verified, you will need to submit the Account Recovery form again. You can do this up to 2 times every 24 hours. 

If your Microsoft account recovery request was not granted or was unsuccessful, please click the attached link for more information: Account recovery unsuccessful 

I wish you best luck with your account recovery. Warm regards,