Incompetence - Customer pays the price!

In April 2016 I purchased an iPhone 6 which was ****** in May 2017 and took an additional contract for an iPhone 7. I then requested a cancellation amount which I subsequently paid into Cell C's banking account using the reference they requested during the month of May 2017. After receiving a statement I then called Cell C to advise them that they have not debited the account for the new phone iPhone 7 and that they were infact drawing the funds from the cancellation amount paid. I spoke to two consultants on that day and both of them assured me that I have simply made an over payment on the account and therefore Cell C will not debit if there is a credit on the account. I advised them (general call centre and the contracts departments) that this was an amount for the iPhone 6 contract that Cell C gave to me and when Cell C wakes up what is going to happen to the shortfall due to the iPhone 7 premiums being deducted for the cancellation amount. I was told (very rudely) that the iPhone 6 has been settled and there is no amount due and I have made an overpayment. I then requested a paid up letter and received the run around eg Call Centre stated I needed to go into a Cell C branch, Cell C Branch stated I needed to obtain it from the Call Centre. Eventually nearly 5 MONTHS LATER Cell C tries to debit my account with a ridiculous amount of R5 000.00. I then followed up on this debit only to find out that it was for the iPhone 6 Cancellation!!!! Since August 2017 I have been on the phone with Cell C, emailing Cell C as well as using family friends (who are employed by Cell C) to come to some arrangement regarding their mishap and finally on the 4 October 2017 I received a call and made the necessary arrangements. I received a reference number, an agreed amount and the banking details to be used. Today (12/10/2017) I received an sms stating the account is in arrears and to top it off Cell C disconnected the line ***! (seems like their right hand doesn't know what their left hand is doing). As a consumer I have shown integrity towards this whole situation, originally coming forward advising Cell C of the billing error etc. Why should the consumer be the one to pay the price for the incompetence? Furthermore I received a statement from Cell C which has a payment of over R4 000.00 made in September 2017 when in fact a payment of R1 800.00 was made. Here again another error which will be picked up in another 5 months time and then the difference the consumer will be liable for and finally, due to the incompetence of Cell C and their staff I now have a bad credit score. Disgraceful