Yea they go off average from previous usage, so could possibly be lower than what u use or also a lot higher depending on the ppl that lived there before.

At our previous house we moved out about 3weeks b4 end of lease and a few months later we got a bill for the electricity for that house (most of that time the new ppl were living there) they realised their stuff up as we were still with the same company and they had details of the call i made when I organise electricity for the new house and asked them to stuff off at the old place, they just stuffed up the shut off, they then ammended the bill when i asked how they would know what was mine and what was theirs they said they went off other averge bills, which wasnt fair as we were no longer in the house most of the time so not using any electricity at all. In the end I just dealt with it and paud it, i was too busy as the time to argue and it wasnt that huge

I hope this bill isnt too bad for you and if it is I would take it further if you dont believe its accurate