My electricity and gas bills are £1500 for 3 months help?

Hi all I just got back from 3 weeks holiday yesterday and was greeted by a gas and electric bill (both Southern Electric) that seem way too high to me.

First the electricity bill. This was for £879 covering the period 13th Nov - 15th Feb apparently in this period we (I live in a 2 bed flat with a friend) used 7175 units at an average of 75.52 per day compared with 23.44 for the same period last year and as far as I'm concerned there hasn't been any significant increase in the amount of electricity used.

Also with the bill was an annual electricity statement which says they estimate our electricity bill for the next year should be £865 making me think even more that something is wrong.

Now onto the gas bill. This was for £606 covering the same period in which we apparently used 1604 at an average of 188 units per day compared to 71.94 for the same period last year. The annual gas statement says that their estimate for the year ahead is £960

I've just noticed both bills are based actual readings where as it seems previously they were based on estimated reading so I'm thinking this might have something to do with it but surely they can't have under estimated it so much could they? and if so is there anything i can do about it?

As I'm sure you can understand as I've just come back from holiday I can't really afford it and going forward with the amounts I pay out monthly I can't see how I'm going to afford it ( I haven't spoken to my flat mate yet but I doubt he'd be able to stump up £1500 at the drop of the hat)

I appreciate anyone who has taken the time to read this and appreciate any help or advice anyone can give

Many thanks

Mark