Comcast online billing and service

I signed up for Comcast's ECObill and online bill payment back in October. Per their instructions I paid that month's bill by check and allowed a month for the online bill payment to take effect. Today I get an automated call that there is a problem with my bill. Turns out they have no record of me signing up for online bill payment and the rep wont remove the $7 late fee. When I pointed out that my payment was late because their systems didn't work all she could say is "but it was late".