Managing personal Outlook.com account settings, security, and privacy
I understand your frustration.
Unfortunately, that is correct. There is nothing that can be done to recover the account once the hacker has modified the security information.
Moving forward, please check this link for more information on how to secure your account and to prevent hacking incidents: https://support.microsoft.com/accounts-billing/manage/how-to-help-keep-your-microsoft-account-secure
Best regards,
Darhyl