cancelation of the contract

After selling our vehicle and phoning to cancel the contract we were told the contract has a few months left. We said tha contract should then be canceled at the end of the term, which never happened. We phoned again an again, but still the debiet order went off every month. We then canceled the debiet order from the bank. Now after a year of the debiet order being stopped they keep on calling. We have explained everything and told them to listen to all our recorded calls, yet they still call. Useless company!!!