Unauthorised debit orders

I entered into a cellphone contract with Cell C during 2015. In October 2017, I received a call that my contract was about to expire and I was asked whether or not I wanted to renew my contract with Cell C. I agreed to renew my contract and I was advised that my first installment would be at the end of the existing contract. A quotation was done (by a person called Neo) and I was offered x2 Samsung J5’s at an amount of R357.00 per month. I specifically advised them that I needed a contract within the price range of the previous contract (which was R303.00 per month) as I was not prepared to pay more than what I was paying for the 2 ********** contract. To my surprise in October 2017 an amount of R527.22 was deducted from my account by Cell C. When I called to enquire about the debited amount I was advised that it included a pro-rata payment. On the 18th of October I sent an email to Cell C again querying the debited amount. I was again advised that I was charged pro-rata. I was baffled by this as this was never communicated to me when the contract was being finalized. I advised that I wanted my money back because I had not consented to a pro-rata payment. I pause to mention that, upon doing my calculation, in retrospect, it has come to my attention that an amount of R498.00 was debited from my account by Cell C (excluding the pro-rated potion). This amount of R498.00 is being debited from my account, without my consent ever since I accepted the new contract. Every single month, an amount of R498.00 is being debited from my account despite the contract being for R357. In February 2018 after going back and forth with this issue, an amount of R700.00 was refunded to me after the audio of the contract advancement (by Neo) was replayed. This repayment is indicative of the acknowledgement that Cell C is ********ly deducting money from my account. With this acknowledgement I was advised that the error would be corrected on the system and my debit would revert to the agreed amount of R357.00. This has not happened, instead I am continually being debited R498.00. I never consented to a debit of R498.00. I only consented to a debit of R357.00. Cell C has repeatedly refused to correct this patent error and every single month I have to go to my bank to reverse the unauthorised debits raised by Cell C. By reversing these amounts, it costs me an additional amount of R40.00 in bank fees. Of late, I have received numerous calls from call centre agents who keep advising me that my account is in arrears and if I do not settle it I will be listed with the credit bureau. I am tired of talking to call centre agents who are unable to sort this issue out. I have requested that I be called by someone who has the authority to address this issue and sort it out, but to date, I am still only called by call centre agents. After 5 months of trying to solve this issue with Cell C I decided to start reversing the unauthorised debits but in actual fact I am no longer interested in continuing with this contract and I have advised Cell C’s agents that I want to immediately cancel the contract and they can come and collect the phones that were advanced as a result because I cannot undertake this exercise for 24 months.