Hey there! Nice to meet you!
Based on your description, your Microsoft account was compromised. The hacker was able to remove the account's primary email address/security info and replace it with their own email address, which is why you received the error "account doesn't exist" when signing in.
Since the security info has been replaced by the hacker, I'm afraid there is no other working method to recover the Microsoft account, and Microsoft Support cannot help either.
Thank you for your understanding.
Best regards,
Darhyl