All I can suggest is that you check that the last meter reading on their bill agrees approximately with the present reading on the actual meter and that the readings on the past bills are correct.
I've written to Scottish Hydro myself in the past as they were judging the whole years supply by what we were using in the Winter months and they didn't seem to allow for the low usage months in the Summer.
If their figures are correct, there's not a lot you can do apart from turn the thermostat either down or OFF to conserve electricity in the future months.
Also, check the previous bills and work out how much electric you used a year ago and calculate for the same amount of electric for this year using the present day cost.
If your figures differ from theirs, send them your figures and ask them to explain the difference, as the amount of electricity used each year should roughly be the same.
I hope this helps in some way.