Vodacom SP

I opened a contract with Vodacom last year in December, and I haven't receive any data from Vodacom, when they bill my account I always reverse and now is affecting my credit score, and I went to cancel the contract they told me to call Vodacom now I'm not getting any help because my sim card is prepaid and they cant help me in store and they cant help on the call.

what can I do to cancel this contract because is not helping me with anything, just ruining my credit score.