Many thanks for all your help.
As you can see there is no decimal point in the reading. I submitted 171.64 to our new supplier EDF and E.ON came back with 18,268 kwh challenge. Also see attached picture of the meter tag where E.ON omitted to put in the opening reading on 19th April. They put in the opening reading for the gas meter tag. Another mistake ? Would I be able to argue in court that the figure of 17,164 is just 171.64 when there clearly is no decimal point ? The manual clearly shows decimal point in its readings.This is my concern.
I think, to be honest, you are being a bit previous, and jumping in with both feet. Send EON a copy of the manual page, which shows the reading of two decimals after the decimal point. Point out what is your normal level of usage, after if they still insist they are correct, then ask for your case to be registered as a formal complaint. If you still get no satisfaction, refer your complaint to the energy ombudsman - https://www.ofgem.gov.uk/complain-about-your-energy-supplier-0