Continues non-approved debit orders

In March 2017 I was due for an upgrade. The sales agent phoned me w.r.t. abovementioned and I clearly declined the upgrade. However I still had one more debit order that had to be paid on current contract. The sales agent aparently noted it on their system. A few months passed and I noticed a debit order has been going down from my account, which I manualy stopped with my bank and it returned. Second month after, same story. Figured I need to go to Cell C Outlet and find out if they did in fact cancel the upgrade. I obviously did not receive a new phone as the sim (previous phone) was ****** in any case, hence the cancellation. So the consultant in store assisted with cancelling the contract on their system as it was apparently not cancelled. I specifically asked him that it is indeed cancelled now and he confirmed. Next month, another debit order. I went to the bank to stop the debit order. Same story the month after. I went to Cell C Outlet again, where another lady consultant phoned the customer care line on my behalf. We engaged in a conversation that quickly turned snotty since the operator asked if I only realised my debit orders going down now. Wow! I told her that they should investigate in the first phonecall with the initial sales person where I clearly stated I want to cancel the upgrade. After a long this and that she agreed and will call me back. That never happened. Next month, another debit order. Phoned AGAIN, same story and same snotty remarks! Again no call back w.r.t. the investigation on recorded calls. Now another debit order!!!!!! HOW DO I CANCEL THIS CONTRACT? I DID NOT SIGN UP TO PAY FOR SOMETHING I DID NOT GET FOR MY ENTIRE LIFE!!! Cell C - come to the party or I will have no choice but to take this matter to the ombutsman.