Forced to pay for a service I don't want

Telkom have misallicated a few of my past payments, I have sent them proof of the payments 6 months ago as I wanted to cancel my service and they won't cancel due to outstanding payments I have followed up for 5 months now for them to allocate the 4 payments that proof was sent and yet nothing has been done, I am forced to pay for a service I don't want due to the incompetence of Telkoms accounts department