I have no account, but Discovery keeps billing me.

I cancelled my card, which was fully paid off. I received confirmation of cancellation. To my surprise Discovery is still billing me for a "credit facility". When I try to log in, I am informed that I do not have an account. The only electronic forim of contact they have seems to be the complaints@ email address. I receive only automated confirmations of receipt from there, no response to my complaint. How do I get them off my back?