I don’t see why they won’t. Shouldn’t be allowed to tell the customers what to do.
We need to get rid of estimates then there wouldn’t be a reason to over pay or underpay.
Most people can’t save that’s the problem.
Your understanding seems rather confusing, you've just answered your own question why energy companies build up balances. They're scared of customers going into debt and having to go through the rigmarole of either sending debt collectors, or the extent of disconnecting the meter.
It's easier for them to build up credit balances and not have to worry about it.