Joke of a service

MTN offered me 30 gigs for 3 months on my top of the 24 months contract i have with them, on the 5th may i got i gig which is for the initial contract i have with them and they billed me my instalment and the additional R100 for the 30gig. When i called MTN two consultant told me that i should have received the 30gig, the one i spoke to yesterday says the IT team has picked up that the 30gig was credited, my question is why would i put in a complaint where else i received ehat was due to me? This is bad service am getting from this ppl and the fact that they literally called me a lie and is on another level, please get me someone to call me i want to cancel my contract ASAP and mind you this is not the first time i am complaining with data