Debt Collections

I have been getting threats from debt collectors the last YEAR. Comcast has said MULTIPLE TIMES they will remove the payment. It was a payment I did not owe. A payment they owed me, actually. Months have gone by and I am STILL BEING CONTACTED FROM DEBT COLLECTORS. Comcast needs to fix this immediately. I am at my wits end. I have given patience, but this is an astronomical mess up.