Bullying by the municipality

In April 2015 City of Joburg decided to replace a water meter for my house and send me an invoice in August claiming they had been estimating my bill for water for the last three years so now they have reversed all the estimations and re-billed me for the 36 months. Which meant I now owed them. So I went to their offices to enquire if what they were doing was legal as according to the law they are not allowed estimate for more than 6 months, and one of the accounts personnel told me it's by-laws. So while I am making payments as much as I could as it now meant I am owing them they send me a statement with two lines for pretermination notices which I never received notices for. What surprises me is that meter readers are at our complex every month taking readings, whereas at the same time the accounts department is estimating for 3 years.