i hope someone can give me some advice.

I moved into my property in Dec 08 and got my first bill from British gas in Feb. it was only then that we realised we were with British Gas Business not domestic.

I paid the first bill at business rates and went to my landlord to make sure they didnt mind us going to domestic. Since June we have been trying to get changed over, but have had serious problems since with them having to recalculate everything to domestic rates rather than Business.

They have now given us a final bill but have added £690.66 on top of that and claim its because they took a meter reading in september and found that they have under estimated our usage.

In the billing Code it says that

Where the supplier is at fault in under-billing a customer by sending inaccurate bills, when issuing a corrected one, the supplier will not collect for any additional consumption (i.e. the shortfall between what was bills and what was used)

but is this only for bills that are more than 2 years old? and because we were listed as a business (even though we weren't) do we still qualify?

we have now been transferred over but it took 6 months rather than their standard 40 days. I'm tearing my hair out so any advice would be appreciated!!!