False advertising

I went to the mtn branch at River side mall in October 2019 to apply for the 10gig day and 10gig night data contract which was R150 but I was told by the consultant that it is no longer available. The consultant told about the 40gig contract which is 20gig day +20 gig nigh for R199, well I accepted that deal but I didn't understand when I received only 20 gigs( 10 day +10 night) and when I enquired I was told that that's what I signed for. They are debiting R199 from me but I am not receiving the correct amount of data which was advertised and when I want to cancel they charged me R700 though I am not the one who breached the contract. The funny thing is that mtn is not in sync with its branches, at the branch they told me that I signed for the 4gig contract but their customer service says I signed for the 10gig contract. I will never ever use mtn as long as I live, I regret ever taking a contract with them it was just a waste of my time and money.