Cannot Cancel a Promo Contract

I upgraded my contract over 2 years ago and received a free sim card with a data contract along with that upgrade. With my latest upgrade, no one told me that I would now be paying for this additional sim card's contract, that I have never used in 2 years.

I phone the call centre to cancel this contract, as now I am being billed every month on top of my normal contract. First time I phone to cancel the lady keeps putting me on hold to allow me time to think about if I really want to cancel, was on the phone with her for about 20mins and every time I have told her that I do not use it and do not need the extra contract, please cancel it. She acknowledges my decision and says it is cancelled. And that I will not be charged for it in the upcoming month.

The upcoming month comes and I am still being billed for this contract. I phone yet Vodacom Call Centre yet again to try and cancel the contract. Speak to a guy who notices my previous call, as these calls are recorded, and says that the previous person I spoke to had not actually cancelled my contract and that because it was a promo contract it is not something they can do in their department. But he advised me that he would escalate this to head office as they can only cancel this contract. He asks me to stay on the line so he can log the request while I am on the phone, which I agreed to. He assured me that the request had been put through and that he has also stated that because he can see record of my previous conversation with the call centre agent requesting cancellation in previous months, he has asked for my account to be credited for the previous month as well.

But I am still getting billed for this promo contract, something I did not want but was given for free, and now being charged for and cannot get out of. It absolutely ridiculous that 3 months after my first phone call and I am still getting billed and I cannot dispute this with my bank. Vodacom needs to be so careful because you losing business because of your poor service.