complete recovery corp comcast comcast modem sales and rental. After purchase they keep saying to return the modem Internet

I have purchased comcast internet services for 3 years then moved my service and was asked if I wanted to but the modem. Which I did then I keep getting emails my service will terminate to the modem due to not paying for the equipment. Which i did I had made phone calls directly to Comcast and they say there is no problem. I received another email for the modem to be returned due to non payment, it has been over 2 years I paid for it and have the bill and confirmation it was paid for. I do not have Comcast internet and never will due to this problem and always the same after disconnecting service and returning equipment to Comcast. I always receive a bill year later but I keep receipts. How is this even possible? Comcast is widely used and I have all receipts but keep getting notices and email scams to return equipment or pay for them when they were returned or been paid for.