I hope you have got things sorted out now and that you and your kids are now warm again. I'm with British Gas who can just as easily double monthly payments. However, if I disagree with the amount, and can show them, by referring to my usage over the past 12 months that they have got their calculations wrong, they will reduce the payments.
I would recommend that everyone keep a close eye on their usage, month by month, and consider whether what they are paying is sufficient to cover it. If you think that you are likely to be in debt over a 12 month period then contact your supplier and ask them to increase the monthly amount NOW, rather than wait until their 12 month review (some companies review user accounts every 6 months). Taking this action should ensure that what you will pay for the remainder of the review period will cover your annual costs and there should be no nasty shocks for you with massive increases. Remember that if you are in debt to them at the review period this amount will be added to what they consider your costs will be for the next 12 months, so that they can recover that debt over your next 12 months. In fairness to the companies there are no added interest payments for the debt accrued.
Personally, I have been advised that my electricity payments will REDUCE from £42pm to £20pm. Having looked at my annual usage I could see that this would result in me being in debt to BG over that period so I phoned them and arranged to pay £25pm which is much more realistic and should ensure that, barring massive increases in fuel costs, I will not accrue any debt so my payments should remain pretty much when they next review my payments in Dec 2009.
Finally, can I just say that no one should have blind faith in the companies to look after your interests. That is your responsibility and if exercised with due care and attention then you should not be faced with huge increases. You should be particularly vigilant if you see news of increases in fuel prices. Contact your supplier and ask if their prices will be going up and if so, how will this affect your costs, and should you consider increasing your monthly payments accordingly. Of course, some suppliers will put of increases for as long as possible, so find when your supplier intends increasing their prices, and check at that time if you require to increase your payments. Or perhaps change supplier, something which is always less painful if you have avoided going into debt with your current company, as all debts will have to be cleared at the time of the change over.