Cancel account

I have been trying to cancel my business account for two weeks, but every time I call in the "RETENTION DEPARTMENT" never answers the phone.  One time I got through, the person said that I reach "OVERFLOW DEPARTMENT" and that the retention department would call me back, but they never did.  There seem to be no online options.  What does a customer do when Comcast makes it impossible to cancel an account?  Do I just ignore the bills?