I'm begging you, just cancel my contract

I have been trying to no avail to cancel an overpriced data contract that came with a Wi-Fi router which I am no longer using, FOR THE PAST 5 MONTHS. Every month y account is debited, every month I call, every month I tell at least 3 different people what my trouble is, before I finally reach someone who tries to convince me to keep the contract. After explaining that I don't need ANOTHER contract besides the one I already have, and I just want the infernal thing cancelled, I get told that it is now done... until next month when it gets debited again. I want the money back for the months that I have been paying for following the initial cancellation and I want the CONTRACT TO BE CANCELLED. Is this an impossible ask or is Vodacom just this terrible?