Vodacom: After months refund still outstanding

Hi, I receive multiple calls to say that I am due for an upgrade on my data package ... multiple times I said no thank you until one day I just said lets go for it. I was under the impression that I was upgrading my existing Vodacom data package, but is was actually a new contract. This happened early August 2018. When I realised that a new contract was issued instead of an upgrade I was in contact with Vodacom and was informed to return the device. Thereafter the contract will be cancelled and a full refund will be made to me. First, I struggled for months thereafter to get this new contract cancelled (only happened in January 2019). Now, I am struggling to get the refund. I have phoned/logged calls multiple times. Every time I need to repeat the same story and every time the query gets closed without a resolution. My last invoice for April still had no refund. I do not want to speak to another Call Centre again. To whom can I escalate this matter to address and resolve? Many thanks