Explain!

I called into customer services twice, coming from a call centre environment, I must say, the service was a VERY terrible experience. I asked both consultants to explain why my airtime disappears neither of them could explain to my understanding, instead i get about 5 sms's thereafter explaining the issue like I'm Stupid! Firstly, ALL my airtime disappears and that surely can't happen with one application that still works on BIS! I'm too scared to purchase airtime on MTN! Its rather sad that you guys don't regard pay as you go clients, I'll be moving my business elsewhere!