Telkom bill for a service they haven't delivered

I took out a 2 year WIFI contact with Telkom in October. The WIFI device was delivered 4 weeks later, but was missing a sim card. I also discovered I was incorrectly subscribed to a more expensive contract than I had asked for. Despite this, Telkom have \activated"the absent sim card and debited me an amount of nearly R500 today. I have tried to cancel my account"