False charges for “digital converter”

Last month my bill showed a charge for a digital converter, which I have never received. I contacted Xfinity through the chat function, and they assured me this erroneous charge would be refunded in next month’s bill. Now I have received next month’s bill, and not only is there no refund but this false charge for a digital converter is STILL there. I am not wasting time every single month speaking to an Xfinity representative on the chat function, only for them to not resolve the problem. Who can fix this properly?