Mtn false pretenses

I have a data contract with mtn . When my contract reached 2 years they did not contact me for a upgrade But continued with it from R250 wich i was paying they raised it to R320 without my permission I contacted call center I was furious so the lady apologized promised me extra data for R169 I was happy I got a shock to see mtn once again took out R320. I'm upset. I want to charge or sue mtn for false pretenses I want to cancel I want my money back is there someone that can advise me on changing these idiots