The good news is that the nonsense surrounding my latest gas bill has now been cleared up. They've issued me with a revised bill, and although it is considerably higher than the amount they were first charging, that was something I was expecting. There still remains the oddity that each time they give me a discount for paying by monthly direct debit, and yet each month they fail to take the money from my account by direct debit.
Anyway, with a bit of luck I won't be paying a gas bill for much longer - one of the things I'm looking for in an appartment is electric heating (although gas isn't an absolute deal-breaker).
I also received my electricity bill this month, which was somewhat lower than I'd expected. Having paid this off, I then got in touch with them, and arranged a monthly direct debit so that I don't need to worry about this again. I wonder if they will actually manage to take the money we agreed.
Of course, a consequence of all this bill-paying is that I'm now broke. Guess I'll have to lay off on buying any silly hats for a while.