I have just left British gas, I had the free boiler cover and set up a direct debit of £110 a month duel fuel.
I was using on average around £80 a month and had £398 credit on my account, yet they stated I was not paying enough, they upped my direct debit without discussing with me as they said they would to £127 a month and were still stating I needed to be paying £145 month.
They claimed the £145 a month was needed due to my gas usage That I was not paying enough for (I use around £20 a month gas but they said I needed to pay £87 a month)
They are an absolute scam company as I was well in credit and could not lower my direct debit back to the agreed amount that I set it at. It was good for the first 3 months.
Also they stopped showing my meter usage on the daily/weekly service and only showed once the bill was issued oh and they charged £80 to leave them. Avoid them is my advice.