They really are useless tossers. We have a metered water supply to our 17 acres about 5 miles from home. When we stopped farming sheep on it about 5 years ago, we turned off the water supply, but told STW that we wanted to maintain the supply and were happy to continue with the standing charge. Ever since then they have been billing us on estimated readings despite it having a remote-readable meter that is in range of the main A46. Even after getting a reading which shows we haven't used any water in 5 years they are still billing us on estimates.
Your idea of a call to the CCW i a good one, I think we'll try it next. Should get a reasonable refund, we've been paying them £60 a quarter for water we haven't been using.