Vodacom Takes Money Even After Your Contract has been Terminated

After switching to Vodacom 2 years ago, I have experienced high data charges, data disappearing, terrible network reception at my home and less than helpful customer service. I therefore decided at the end of my 24 month contract to switch back to another cellular provider. My contract with Vodacom ended on 5 September. I contacted Vodacom a month before to notify them that I would like the contract to terminate on that date and was advised that upon termination, I would be switched to prepaid. I received an sms confirmation that my request had been received. I have subsequently gone through the process of porting my number to a new provider and again have received confirmation from both Vodacom and the new provider that this has been successful. Imagine my surprise when logging into my online banking today to find that Vodacom had taken an amount of R984.51 off my account on 1 October 2018. My contract terminated on 5 September so there is no reason for this amount to have come off and this was higher than the amount debited for my contract when I DID have a contract with Vodacom. On trying to call Vodacom to resolve this matter I of course get an automated message saying they are experiencing higher than normal call volumes and to try back later (when I will no doubt get the same message). I would like this matter resolved immediately and the funds refunded as there is NO reason for Vodacom to be taking any more of my money.