Re:Massive Electricity Bill
Sounds like it's a back log from previous bills which were grossly underestimated. Give them some grief. I got £500+ knocked off a bill after a lengthy argument with N Power. I switched to them after they said they'd be cheaper, ran short by £700 in ten months.
They do the minimum possible to keep themselves the right side of the ombudsmen, but flout rules where possible. You'd expect any business expert, with millions of customers to be a little better at estimating.
They're only legally required to read a meter once a year and don't do anymore as "it would be too expensive", then declare annual profits circa £600m.... Blatant profiteering.
There's an offical complaints channel for the industry. They're fairly helpful. Google it.