Bad service and billing

Changed address a month ago and paid as per usual. Cancelation is now still pending a month later and my account was double debited. Agent I spoke to who was not helpful at billing advised that it was a pro rata rate which was not communicated to me when changing my address, furthermore looking at account invoices and statements there is no mention of the pro rata fee. I am happy with the service but not the billing. Not happy with paying for the future and still being double debited and a month later the previous cancelation has still not been completed or dealing with an agent that just wants to prove a point and talk over the customer without an attempt to help effectively.