Airtime being deducted while having data

I've noticed that my available airtime is decreasing faster than it should.<br> I this morning checked my airtime (and data) balance using *141#, I had just under R900 airtime and 411.22MB of data. I proceeded to use apps that use mobile data, when I was done, I checked my balance again and was left with R759 airtime and 411.22MB data. <br> I tried calling the call center (multiple times), but, roughly 5 seconds after selecting 0 to speak to a consultant, the call is ended.<br> I have always been a happy MTN customer and would hate to move to a competitor because of BAD service.