Managing personal Outlook.com account settings, security, and privacy
Alright. The next step is to contact Outlook support which can check and remove the association with the hacker from the backend.
Please contact Microsoft Support for further assistance.
Please go to the https://support.microsoft.com/contactus page
Type "Billing" and press Enter.
Please click on the "Contact support" button at the bottom.
Select the Product and Category for support based on your requirements.