BEEN COMPLAINING FOR MONTHS FOR NOTHING!!!

I have been complaining for months now about my airtime disappearing, at first someone came back to be but quoted dates in 2014 which isn't even close to the time frame that I have a problem with. Called the call centres a couple of times and all they say is the will log it and someone from their technical department will get back to me. Up to now no one has came back to me. The first person did check for any content subscriptions but there is nothing. Then another guy said that my internet usages takes my airtime which I cant see that it is the case because I always have data on my phone. Then the last time I called the lady claimed that there is no sign of any queries being logged? Either the people is who help me is *********** or MTN is just not up to speed with customer services. I cant always attend to phone calls and have asked that should anyone need to speak to me to phone me on the number in question after 4pm in the afternoon. The amount of airtime that went missing unexplainable in the last 6 months is probable about between R200 to R300 if not more. For how long should someone complain before the problem is resolved? Not the first time MTN delays in their feedback.