Wrongful Billing

I live in an RDP house in Randfontein and I pay rates every month depending on how much the account reflects (which hovers around R500 per month with the water usage of an average of R63). However, for the month of April 2015, I have received a bill of R2471 (with water usage reflecting R1441). I cannot begin to even fathom where the municipality can ever get to such a conclusion. Can someone assist?