Cell C Bungling on *** - Customer ID ***

I have been a loyal Cell C customer with a total of 4 contracts with Cell C for years. In 2021 June I changed my Bank details, and I was unable to inform Cell C timeously for the debit orders to come through my new bank. Cell C was therefore unable to obtain all their dues, as they were successful in obtaining funds for the one stand-alone contract. On the 29th of June 2021 I obtained Cell bank details and subsequently made an EFT payment for the 3 linked contracts, a sum of R692,98. Cell C however continued sending me notices to the effect that my account was in arrears, and I emailed them proof of payment. 2 weeks went by without any confirmation of receipt from them, until eventually on the 14th July I received an email confirming that payment was received and had been allocated to the reference number quoted. I breathed a sigh of relief, but to my utter dismay on July 25, Cell C debited my account an amount of R1455, over R700 above what they were supposed to debit for the 3 linked accounts! Since then I have been calling them, emailing them repeatedly for the refund, but all I get are auto-responses alleging that someone would get back to me within 24-48 hours, but no-one ever does! When I call their customer services department they promise that they have made an escalation on my behalf, and that their back office would be in touch with me, but that also never happens. I am considering blocking Cell C from assessing my back account until they have resolved this matter, or ultimately terminating all the four contracts before their expiration dates. If I have to go that route I shall refuse to pay Cell C any early cancellation fees for the way they are messing me up!