Sending, receiving, and organizing email in Outlook.com
Hi. I'm Brian.
Unfortunately, the most common cause of the error you describe is a compromised account for which the hacker added their own address and removed yours. When an address ending in a Microsoft domain like @hotmail.com is removed from an account, that removal is immediate and permanent. Moreover, the address becomes permanently disabled and it can never be reenabled. I wish I had better news. If you had any payment cards associated with that account, contact the issuers and get your cards reissued right away. If you used that password with any other account, immediately log into the accounts and choose a different password. Every password you use should be long, complex and completely unique.