Hey there! Nice to meet you!
I'm sorry you are experiencing this.
The only way to recover a hacked account is through the official Microsoft troubleshooter guide:
If the account recovery web form doesn't work, and since the security info has been replaced by the hacker, I'm afraid there is no other working method to recover the Microsoft account, and Microsoft Support cannot help either.
Also, based on your description, the hacker accessed your account 30 days ago and requested a security information change, which requires a 30‑day completion period. The successful change indicates that the 30‑day security has now been completed.
For possible reasons as to how your account was hacked, this was properly explained by the user David Warner from this thread: https://v4.hkg1.meaqua.org/answers/questions/1195380/why-was-someone-able-to-access-my-account-despite
Thank you for your understanding.
Best regards,
Darhyl