spuddy:
I believe its unlikely to have been such high electricity consumption in a gas heated apartment. Is it possible/practicable to get back inside the building and take a photograph of what you think was your meter? This has some of the characteristics of a meter database problem, either initial reading, final reading or wrong meter.
If you have not been convinced by the EDF explanation dispute the issue strictly in accordance with the EDF complaints procedure. If you remain dissatisfied after 8 weeks (I think) you are then entitled to take the issue to the Energy Ombudsman or other alternate dispute reolution service.
Do it quickly, you have nothing to lose.