Dad's elec/gas supplier?

I've had the solicitor on on Monday asking if I have found out yet who provided my dad with his electric and gas where he lived. I have been in contact with British Gas but they said it wasn't them, so I have no clue. Maybe I changed it over when he moved, I can't remember as so much was going on, but he could have changed it again and not told me. No paperwork found in his flat, nothing on his statements.

Does anyone know of one number I could ring and they would know who his supplier was? Save me ringing all the companies up as what he might owe will probably be less than my phone bill to find it out! He sat without lights on, just the tele and put a quilt round his legs to avoid putting the heating on, even though he could well afford it, and I used to tell him to get it put on to avoid illnesses but he wouldn't take me on. Thanks in advance if you can help.