Billed for data although I have surplus

I received my last statement only after requesting it to be resent, seeing that my bill was way more than usual. Upon opening it I saw the most expensive item billed was for data to the amount of R 441.27, and on the same invoice a surplus of 1. carried over: 1648 MB + added this month: 824 MB. And then Used for the month: 456.50 MB. <br> How does 2472 MB surplus - 456.50 MB usage allow for charges for data???<br> <br> I have now been sent from billing- to technical- to data department to no avail for 16 days. Is this the level of customer service you provide?