Billed for handset which was already paid off and refusing to refun me

Case Number : ***

CellC billed me for my device (handset instalment) from 1 Nov to 30 Nov as per my Nov statement. My contract ended on 4 Nov 2022 (i.e. my divide was paid off on 4 Nov). The amount is R826.09.

I logged a call on 21 Dec 2022 for this incorrect billing. They said a consultant would contact me within 24 to 48 hrs...never happened. I followed up on 3 Jan and then someone called me. This person tried to convince me that I was wrong and that they didn't owe me money. I asked him to open up my original signed contract and look at the end date and then look at the statement and tell me I am wrong. He then agreed and said he will escalate it and that their finance department will call me to confirm banking details for the refund. Someone did call me again on Monday 9 Jan 2023 but not for a refund, it is back to square one where they are trying to convince me I am wrong and this person continued telling me about the Dec statement and there's no device instalment on it. The more I asked him to look at the Nov statement the more he was adamant that I'm wrong. I asked him to send me an email so we can correspond in writing and I can send him the info for review. He confirmed that he will do so...today is the 16 Jan 2023 and I have yet to receive the email.

I then sent another email on 9 Jan 2023 with snippets of the statement asking when I will receive my refund. Well like I say today is 16 Jan and I have not heard from anyone. Almost a month now after I logged my initial query and they are sitting on my money.