MTN has just charged me a contract client for over 20 years R 200 for 3gb of data???

I've just been fleeced out of R 200 for 3gb of data? Despite having 38 gb available on my contract. That balance was confirmed earlier this afternoon? At no point did they offer to upgrade my data contract to an uncapped option. When I tried online I was told my current contract only expires in November? Surely in terms of the Consumer Protection Act, I should be able to amend my policy with due notice? R200 for 3gb of data is highway *******. It's a blatant abuse of power? Why can't I simply upgrade to uncapped?