Thanks for your help :).
It is Scottish Power. We moved into a new-build about a year ago and still haven't had anything from them, which is really worrying because we have no idea what this house costs to heat!
Any email/postal address would be great if you have one. So far they have ignored all of my written communication.
By the way - if we accept the Ombudsman's decision (even though it's very vague and we still have no idea what the numbers are)... Can we still take the company to small claims court for expenses? Or will it put us in a weak position if we accept the ombudsman's offer?