My “@me” email account stopped receiving emails, why?

One day my email account associated with my Apple ID, Which was an “@me” email account that had worked and which I had made my main email account suddenly had no emails and doesn’t appear to to exist. It asks for my email provider, I figured iCloud would be it so I did my b******2@me.com and password and it says “email already in use on this device. I feel like it’s taking me in circles. It never used to do this. It was just automatically the @me email account on iPhone that was so convenient and easy. But now I cannot check it nor can I make it my email address on iPhone.