Unauthorized charges on bill

Every month since I got ATT service a year ago I have had a charge from "Excel Telecommunications" on my internet bill for a long distance service that I never signed up for.  In fact for the first six months I only had internet service (no home phone) so why would I need long distance?  Every month I have to call ATT and spend an hour getting the charge removed but then it  is back on the next month.  ATT tells me to call Excel Telecommunications to get them to cancel the service, which I do every month (another hour on the phone) and Excel tells me they have no record of me being their customer so they can't remove me and they say it was a mistake by ATT but ATT keeps telling me that Excel has to cancel a service I don't have.  This is so frustrating!