My Microsoft account was hacked and the attacker changed my primary alias. I can no longer sign in.

@Hanna B said

Customer support is absolutely appalling ... you can't fill in any forms because your primary email address no longer exists.

Your first complaint is caused by your second complaint.

Microsoft has implemented Account Recovery in such a way that if the hacker:

• Replaces all aliases
• Replaces all verification methods
• Enables Two Step Verification
• (All of which they can do in seconds)

Support is helpless, and they know it. So they often just give you a link to a "My account was hacked" page and close the chat.

Has anyone managed to resolve cases like this

Not that I have seen. With one exception, Xbox accounts where you can provide the hardware identification originally tied to the account.

Customer support is absolutely appalling. You are sent around in circles and you can't fill in any forms because your primary email address no longer exists. In the meantime, the hacker has access to all the personal data and files, while it is impossible to get through to anyone at microsoft.

Has anyone managed to resolve cases like this, and if so, how did you proceed?? Thanks

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.

The only methods to recover a hacked account are covered in this article.
https://support.microsoft.com/en-us/account-billing/how-to-recover-a-hacked-or-compromised-microsoft-account-24ca907d-bcdf-a44b-4656-47f0cd89c245