Being billed for a service you terminated

August 2017 I submitted cancelation form for the B315 30GB contract I had. I was told cancelation to be be effective after 21 working days. Its been three months now and I'm still being billed for service I no longer use, dispite the countless efforts I have made. Now I'm being told that I cannot cancel the contract cause my account is in arreas, which I find unfair have all the attempts I have made to cancel this contract. No one at the telkom store seems to be able to assist me. The least they could do was advise me to share this awful expirience and hopefully I will be assisted.