Inaccurate billing

I have been overcharged for water from March (when I move into the property) to September because of estimated rather than real water readings - then went through a whole exercise to have that corrected. Now (Dec) they again estimate my water usage at 31 kiloliter a month rather than the less than 8kl that I use, resulting in in inflated account of almost R1000.

How can they not use the previous months usage to do a proper estimation. Extremely frustrating to receive no service when you are paying rates etc. of R3k per month.