One gig of data doesn't cost R14000

On December 30, I woke up at a music festival in the Drakensberg to find I'd been charged nearly R16000 on my phone account which was impossible. Eventually able to get through to Mtn I saw they'd charged me nearly R14000 for 1 gig of data which can be bought over the phone for R160. I was not surfing the internet out of bundle. They just charged me well above the set price. They then said they were wrong and would fix the problem. They didn't cancel the payment. My bank account was in negative. Eventually Standard Bank reversed the payment as not enough funds were in my account and charged me a R110 honouring fee. MTN still hasn't corrected the billing and they have threatened to cut my phone off if I don't pay nearly R16000. They keep on sending smses and reference numbers and say things are being escalated. I want to cancel my contract but I'm paying a phone off over two years and it hasn't been a year yet.