Overcharging Ex-Nashua Customers

Afternoon. I was previously a Nashua customer. We were then moved to MTN. The Billing Department? Disaster. I constantly received an invoice saying that I have over-spent each month. I'm suppose to pay a total of less than R400 each month. But every time I receive a Bill, it comes as high as R800. I'm on Open-Line. I'm not new on that package. So, I know how it works. I closely monitor my spending well, and even if I check my airtime it will show that I still have credit left. Yet customer services will say that I used all my airtime and I will be charged out-of-bundle rates.<br> So basically the problem that I have is, even after MTN credit my account with my monthly allowance, customer services will still say I dont have airtime, hence I will be charged out of bundle. This has led to me being over charged, because they say that I dont have airtime, even though it shows on my phone.<br> <br> MTN has only credited me for one month, what about all those month that I have been over charged? Why is the customer care not seeing my airtime, while I see it.