Managing personal Outlook.com account settings, security, and privacy
Hey there! Nice to meet you!
I'm sorry you are experiencing this.
Based on your description, 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 that the 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Since the security info has been replaced by the hacker, I'm afraid there is no other working method to recover the Minecraft/Microsoft account, and Microsoft Support cannot help either.
Thank you for your understanding.
Best regards,
Darhyl