I've been with British gas since November 1975. Later on I went dual fuel with them, (previously Yorkshire Electric). Never had a problem and never had a substantial price hike. I think my bills are quite low compared to some.
Remember on the gas side each 1 degree on the room thermostat is 10 percent of your energy bill.
I've fitted my Hive in the lounge as that's where TV is.
Saves a fortune but you can't have a fire on in lounge as it would shut it down. 19 degrees is plenty.