Don't get me started on British Gas - too late, you already have.
After we moved house we had a nightmare with BG. They would not accept my meter reading and kept sending fresh bills, wanting more money. We can only presume the new owners were sending a final meter reading which was greatly different from ours.
We were eventually able to show by analysing the past five years bills (I keep everything) that our final meter reading equated to the average gas usage, and that the other reading they were trying to use was way out of line.
Of course, no apology or compensation for the time taken to sort it out or the harrassment by BG.
Moral of the story - if at all possible get the incoming owner to agree the final meter readings with you before you send them off to the utility companies.
In "the olden days" utility companies would send a meter reader round on the day of moving, so the reading was oficial and correct, sadly not done anymore.