Poor customer care and airtime going "missing"

Out of my 75 minutes a month I have used 18 minutes so I should have 57 left. Vodacom system says 32 left so that's 25 minutes missing. This happens each month. I make very few calls and don't "sit" on the phone so they are very short. After 2 years contract I should have a few hundred minutes built up. Vodacom customer care cant help me unless I pay for them to send me a itemised billing schedule, as the customer care consultants are unable to access details of my calls on an " open" account, only on a top up which I do not have. So basically I have to pay to query something at Vodacom. Pathetic to say the least.