MTN ****ming unaware customers

I had a router contract which ran from 27 August 2021 to 26 July 2023 for R1,059/pm and increased R1,093.28/pm - the increase being their "service charge". On 26 July 2023 when the contract ended, I cancelled the contract ("gave a 30 days' notice" per their requirement). I received a SMS from MTN on the same day, 26 July 2023, at 17:32 pm confirming my cancellation. I was charged an out of contract tariff of R1,568/pm for the period 27 July 2023 to 26 August 2023 given the fact that I was charged a prepaid rate - I get this aspect and I was debited this amount on 01 August 2023 (partly in advance).

On Sunday, 27 August 2023, I received an invoice and a statement of account for 27 August 2023 to 26 September 2023 and R1,468/pm being due on 01 September 2023. This is my dispute; I gave notice on 26 July 2023 which means that they have billed me for this on 01 August 2023 for the 30 days' notice period 27 July 2023 to 26 August 2023; the contract has now ended.

MTN claims that the cancellation was not closed internally, that is none of my business, I gave the required notice and received an SMS confirmation of this cancellation on 26 July 2023. If their employees did not complete their job that is none of my business. They now say it was closed today, 29 August 2023, and I must keep references for a future credit, this is after a close to 2-hour marathon calls I had this morning with 9 or 10 people transferring me to and fro on the call. I disagree with this, I have fulfilled my obligations and already paid a prepaid rate for the notice and I cannot be held accountable for their negligence and be charged twice for a notice period. [References *** for the 29 August 2023 MTN cancellation and reference 1-*** for the 26 July 2023 cancellation].