unhappy customer

Mtn has a free airtime service which is aquired when you call, whenever i get the free airtime i never get to use it to my satisfaction as it charges from my own airtime even when i am calling other mtn numbers.<br> <br> I called 173 to get assistance but did not get help as they want me to call back, why cannt they log a call and look into my quiry then call me with an answer that will satisfy me.