Sending, receiving, and organizing email in Outlook.com
Hello NerteX, thanks for posting this in the community.
It sounds like your account may have experienced unauthorized access or a security compromise. The fact that an unknown phone number is showing up during password reset suggests that the recovery information was changed by someone else.
To try and recover your account, use Microsoft’s Account Recovery Form at https://account.live.com/acsr. Enter the email address of the compromised account and provide an alternate email address where Microsoft can contact you. Fill in as much information as possible, such as old passwords, subject lines of emails, Xbox details, or anything you remember. The more accurate details you provide, the higher the chance of recovery. Account recovery unsuccessful
If you cannot recall enough details, Microsoft may not be able to restore access for security reasons. In that case, the best option is to create a new Microsoft account and secure it with a strong password, updated recovery email and phone number, and enable Two-Step Verification.
Kind regards,
John Oli