Managing personal Outlook.com account settings, security, and privacy
@Panupong Suwan said
I have submitted account recovery requests multiple times—most recently today—but so far, I have not received any email response or updates. How long does it typically take to receive a response to a recovery request?
Usually the Account recovery process will respond almost immediately. Have you verified the email address you used on the form is correct? Checked for a response in Junk/Spam? You may not receive any response after multiple feiled recovery attempts. But you should have received at least one. All I can provide are the suggestions from Microsoft for am Account Recovery Unsuccessful
https://support.microsoft.com/en-us/account-billing/account-recovery-unsuccessful-dc56c3e3-dff0-4ed5-8edb-60290eea6b53
In a situation where the backup email has been changed to one belonging to an unauthorized party, are there alternative identity verification methods that do not rely on the altered email or phone number?
No. If you can not complete any of the verification methods that have been established for that account, your only recourse is Account Recovery.
Is there a way to escalate this case? This is clearly a case of account takeover, not simply a forgotten password.
No. Microsoft Account Security is an automated process. Microsoft Support Agents can not unlock an account, reset your password, or change any Security Settings no matter what documentation you can present.
used for both work and Xbox
You can also try the Xbox Account Recovery Form. Sometimes that one may work when the Microsoft Recovery doesn't
https://support.xbox.com/en-US/forms/recover-your-microsoft-account
I am sorry. I know that losing access to your account is more than just an inconvenience, it can cause real hardships. I wish I could give you another answer.