Real airtime chowed after buying MTN to MTN minutes and calling an MTN number for 45 minutes

I bought 60 MTN to MTN minutes, then made a call to an MTN number. After 45 min my call was cut short because I was told I was out of airtime, so MTN actually charged me airtime instead of taking from my MTN to MTN minutes which I had bought for the specific cause of calling that MTN number to have a long conversation. What is worse if even when you dial 136/135/144 it doesn't give you the option to speak to a consultant anymore. My airtime was chowed..