Inability to close contract.

Took ou contract several years ago on cell phone. Unable to close account. They say you can only terminate account telephonically which I have done on numerous occasions with no effect. I have a debit order in place which goes off every month. Bank won't stop it unless company do. There is no proof given of telephonic transaction to terminate contract. So can not really phollow up. If you do you get the run around. They won't accept emails or written requests. So it appears to be true that you can never cancel a contract.