Yes Margo, they supply both gas and electricity for me. I pay by fixed monthly direct debit. The only company I have ever had billing problems with is British Gas. They couldn't seem to be able to grasp the concept that their customers generally use more energy in the winter than in the summer and instead of charging me a monthly fixed amount across the year they wanted to keep adjusting it when my payments did not match my usage.
I am fortunate in that I know to within +/- 5% how much energy I will usually use in a year. It rarely strays more than that. I can therefore arrange my deal on the number of Kwh I consume. I also keep tabs on my monthly usage and can easily and quickly spot any anomalies. For that reason I'm unlikely to suffer any billing problems (which, to be honest, are about the only problems I can imagine an energy supplier causing me).