Dissatisfied customer

I'm really disappointed with MTN, I cancelled my contract, no one told me that I'm going to forfeit prepaid data that I purchase on prepaid, I called, they told me to write email which no one responded till today. Today I purchased 55 min MTN to MTN but still unable to call MTN numbers with the minutes, the call I made used the last airtime that I had and left 5min which I am unable to make calls from and those minutes are expiring midnight