billing: estimated consumption of electricity

Your estimated consumption on you invoice is utter ****. Can you not develop an app where the customer can input his monthly meter readings and get a correct bill. I have been hit with 2 large bills 2 months in a row. What a financial inconvenience especially around the festive period. Surely you guys can develop a better looking invoice with a better layout not to confuse your customers. Unless that’s what you guys want to do, confuse and rob your customers.