Hello, thank you for reaching out to Microsoft Q&A.
Do you receive the error message “This account doesn’t exist” or “The username is incorrect” when signing in to your Microsoft account?
Have you tried recovering your account using the Microsoft self-help recovery article? See,
How to recover a hacked or compromised Microsoft account
Also, if you get the above error message when signign in, please click the link below and expand the " If you still see 'We couldn't find an account with that username." section to get in touch with the support.