Hello Xzavier,
Thank you for posting your question here.
This usually means someone added their own backup email or replaced your primary email, which strongly suggests the account was compromised even if your password stayed the same.
Here's a form you can fill out that will go to a team specially equipped to handle scenarios like this. Please fill out this form https://aka.ms/recovermyaccount you should get an email response within 4 hours the latest. The team on the other end will help work through the issue with you. Also, may I know if you already use this link for account recovery request or a different site.
Let me know if you need further assistance, feel free to ask me by clicking "Add Comment" or "Add Answers" if you cannot add comment so your response will be visible. Thank you and I appreciate your effort.
Best Regards,
Ian Patrick B.