Cancelation of contract

I have been trying to cancel sim card contract from July. I have went to a Durban CBD😞Pavallion and Gateway stores they keep driving me away to the next store. Last store they gave me call center number and they said they do not cancel contracts.

I called the number *** there is no answer I would stay for 30 minutes and more till I exhaust airtime. They keep on debiting me. Even if I cancel the debit. What do I do in this case?