Im liasing with a different supplier on a similar issue atm, they REDUCED my direct debit instead of increasing it on the back of some meter readings as they accidently only looked at the Gas, and not the combined, thus making it seem I was massively in credit. This came to light when i moved out ~4 months later and i had a bill for £300 despite being told on previous bills i was in credit!
They're allowing me ot pay it back over 3 months but I'm pushing for a concession of some variety as gesture of good will, as it was definitely their mistake that caused me to be behind, not a lack of communication (ie not enough meter readings)
Tom.
PS we used 17 units per day of electricity averaged over 228 days, and that was with 3 people in a house. I had a plasma tv on a few hours a day, a PC on 24/7 and for about half of it a dual quad core xeon server on 24/7, and my "lodger" had similar (lcd tv and a dual p4 server iirc) so not very light users really.