Bad service MTN Cresta

I took out a contract in December 2014. My sim card was never rica'd until roughly end of July 2015. After fighting and arguing with MTN they finally rica'd my sim card. I have not received all my monthly min but I am paying them almost r400 a month for my contract. I was informed by the customers care my minutes falls away after 5 months. I have phoned numerous times , I've been driving up and down from branch to branch asking about my monthly minutes that I'm not receiving. I am short of 400 minutes that I paid for but never received. I am tired of phoning and driving up and down for answers. I always thought MTN was on top of there game but I guess we all just a number. I don't know who else to complain to or to get decent feedback regarding all my minutes I didn't receive. I'm been told all the time they don't know what's wrong or I will be phoned back. And 3 months later I still don't have an answer. The MTN store and Cresta should have Rica'd my sim card in December why should I fight with the store to have it done. I want all my minutes that I paid for monthly and never received