Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
Thank you for the information.
Since you mentioned that you haven't accessed your account for more than 15 years, I'm afraid your account may have already been deleted/closed due to inactivity.
As stated by Microsoft, accounts that have not been signed in or have been locked for more than 2 years will be deleted due to inactivity, and they can no longer be recovered: https://support.microsoft.com/topic/microsoft-account-activity-policy-7c0a9fa7-0982-b7c6-fd72-df852b63699f
Thank you for your understanding.
Best regards,
Darhyl