Non-existing offers and BAD service

Mondo and MTN are selling non-existing offers to clients. I got a call from a guy says his from Mondo and offered me two sim cards for data. One had to have 20 Gig which will be 10 Gig day and the other 10 at night for R99. He offered me another one for 40 Gig which had to receive 20 Gig for day and the Other 20 for night at the price of R169. I just found out that those were pure BIG lies. Both sim cards are getting ONLY 6Gig, how ridiculous is that? He even **** to me and said I will be able to make change of ownership on one of the sim cards as I was taking it for my sister. When I try to call MTN to make change of ownership so that she can pay the sim card her self, they say it's impossible. This is my first time using MTN but I don't think I'll ever use it again or recommend it to anyone. What a BAD service. I tried cancelling this contract and was told am not able to. This is really ridiculous