Repeating annoying 'You only have enough airtime for a short call' during call voice

I know other people also have the same issue, you are on a call and you get that annoying voice saying 'You only have enough airtime for a short call, please load airtime' repeatedly while on the call!!! Even though I do have airtime to continue the call for two more minutes. The voice repeats until your airtime is gone. I liked being on MTN but this is enough reason for me to switch. I call them, tell them about the issue and they tell me there is nothing that can be done, I just need to drop the call and call again!! I was trying to contact my insurance, and I was on a queue for several minutes, and when someone finally answers my call, I get this annoying voice. Can this please be an option!!