I received and paid a bill from Npower for my gas on the 20th October which was estimated at 22344 units. I checked my meter and found the units charged were higher than the usage but didn't worry as I knew it would sort itself out on the next bill. However today I received a further bill from them for £21.49 which was for an actual reading of 22335 taken on the 6/11/09 and was less than the estimated reading on the 20/10/09.I contacted their customer services department and was told this is correct and the young lady tried to explain the higher and lower unit charges which I don't understand. I do however feel that their meter reader should have read my meter prior to the October bill being sent out so as to avoid confusion. I am a pensioner and living on a fixed income and don't expect two bills in one quarter. Needless to say I will be looking for a different provider for my gas in the future.