MTN cant honour contract conditions

My contract was about to expire and had no intention of renewing it since i wanted to port the number to another network. I was then told that if i renew my contract i would get 12 Gig of data for R99 per month. Also my daughter's contract which was almost expiring would be renewed and she would get the same deal. I automatically agreed as the deal was good. Both numbers only received 24Gig the first month and thereafter i am reciving 2Gig and paying R137 per month. I tried calling their call centre where they referred me to the contract departments. I now want contract K*** cancelled since MTN cant honour their side.