Horrific battle to cancel contract- and then billed almost 4 times my usual debit AFTERWARDS?!

I have been having the most frustrating saga with Vodacom trying to cancel my two contracts that expired in December. I phoned them every month (incl December) all the way to April, asking for the contract to be cancelled. After many calls, many ill-timed sales pitches (every. single. time.), and being billed for 4 months longer than I could afford in the first place, they finally cancelled it mid-April. I made a point of checking whether I had any outstanding balance, and the agents assured me more than once that there was nothing outstanding. But lo-and-behold, at the start of May, a Vodacom debit goes off my account for MORE THAN 3.5 TIMES MY MONTHLY CONTRACT AMOUNT.

And of course their "Contact Us" numbers on their App don't give you an option in any of them to speak to an agent (I tried all of them). So I can't even get through to talk to anyone about this. The best description for my feelings is exasperated. This feels a lot like ****************.....