Mtn is a *******

Mtn offered me an upgrade on my data contract last year November from 20gig anytime data and 20gig night time data, which equals to 40gig monthly. The new package I was offered was 30gig anytime data 30gig night time data equaling 60gig a month where I was told I'd be paying R179 monthly. To my surprise instead of receiving 60gig I received 20gig I.e 10gig anytime and 10gig night time data for R179, this meant that my contact was down graded. I contacted mtn on several occasions but I was sent from pillar to post without any solution. I asked them to cancel the contract and they asked for contract cancelation fee which I'm not willing to pay because I have honored the contract on my part. The data they are giving me now equals the package I was on when I initially took the contract four years ago where I was paying R149 monthly. This is really frustrating me because I never thought they would rip me off like this because they have been good to me over the past four years. I'd really appreciate it if mtn or anyone can help me solve this problem as it has been seven months now without a solution