MTN - disappearing free minutes

I have a contract with free minutes, data and sms. For the last couple of days, I receive an automated message that I only have airtime for a short call. I phoned earlier today, and Anna assured me she will reset it, as I have 6500 free minutes available. This needless to say didn't happen. Please ensure the log has been submitted to establish how much airtime has been used for calls even though there is more than enough minutes available.