Horrible service from Vodacom contracts department

I got a cellphone contract from Vodacom in 2021, during the second year of the contract I decided that I wanted to settle it. I was given a settlement amount which I paid at a vodacom shop.

I then sent through the relevant documents to vodacom including the form. Right now in 2023 I started receiving emails from them that I owe them. I called the call center numerous of times and it was only then that they said the contract was canceled. My question is, what was the settlement amount for and why is a contract that was canceled back in 2021 still owing ? I then asked for this to be investigated and was promised a response, close to a month later I still have not received a response and now I am Being contacted by debt collectors. I refuse to pay for something that I am not using and for which I asked to be canceled.