Telkom contracts are very bad

I have taken a Telkom data sim contract and after 4 months of using them I wanted to cancel the sim. I phoned their customer line, they failed me, I phoned again they asked me to cancel it online but it never succeed. I was then told to go to the nearest shop but i was never assisted, I phone Telkom and told them I'm fed up of their tricks and they told me they will cancel it with a penalty of R800 I told them to cancel it and I will pay it and I want nothing to do with them, Telkom are opportunist since they got a licence to be a mobile operator and they chow us.