Can't enter my admin area

When I wanna log in with my username and password on https://wordpress.com/wp-admin I get this massage:

Admin not a valid username on WordPress.com, please try again with the correct username.

Admin always has been my username. I never changed it. Now all of a sudden it does not work anymore and I can’t enter my site / admin area. I tried an account recovery but that did not help.

Any idea?

PS: I even had to create a new account / register in order to post something here.