@MissChief, £213 credit isn't a a lot all for a ~£100/month direct debit payment (assuming that is in the right ball park), if anything I'd say it's below where it needed to be going into winter. Remember, its still autumn the 3 coldest months are yet to come.
So what? Why should we be in advance credit with them, holding MY money and earning interest on it (or hedge betting on futures contracts like they do).
To use an analogy its like buying a RTX4080 from OCUK for £1500 for delivery tomorrow and Gibbo says you can't buy one until your account is £750 in credit a month in advance !