Please can you explain calculations as displayed on the bills please. E.G. if it says a customer has used '90 kWh @ 12.91 p/kWh', does that mean you multiply 90 by 12.91? If so the total should be 11.62 but on my bill I have been charged £11.66. Please explain as all the calculations on all my bills don't seem to match the results of your equation.