I am billed by the hundreds of cubic feet (CCF) I use,
Not by British Thermal Units.
A ‘standard’ cubic foot of gas (the mass of gas that fills one cubic foot at 70F and atmospheric pressure), has around 1000 btus in it.
Your bill will have a ‘billing factor’ or ‘energy factor’ or something like that, a number near 1.00 that adjusts for the heat content of the specific gas they’re selling you.