I'm with British Gas.
Re: billing, BG has recently installed a new program as there were glitches in the old system. It's still not perfect.
On one page they inform you of the amount you owe which differs to the figure on another page. Only one includes 5% VAT.
Also, I don't like having to apply a formula every time I want to work out the cost of electricity.
I find the only way to get some action is not to bother dealing with agents, but immediately make a complaint.