His direct debit is over £200pm, yes?
But how much is it costing him?
The reason I moved to paying the bills as they came was because Eon kept insisting I needed to pay £400pm. When my actual spend was more like £50pm. There was no talking to them. I went to paying bills only (still by DD, so still got the DD discount) and it was a YEAR before I actually paid anything as they were using up the credit first. (I know I am lucky that I don't need to worry about monthly budgeting and getting into deficit)
It's actually scandalous how they do it. I lost patience after having two £1k refunds from them and they STILL wouldn't put it down. I could show them spreadsheets of usage going back years, but no.
So, ignore what you pay to the provider, and work out the cost of what you use. It's quite enlightening. I moved to Octopus, and their app is great at telling you how much each day has cost (linked to my smart meter). So it's very easy to keep track of.
My mum's house, in the current cold snap, which is far bigger than mine, was £167 last month.
I know people use more for lots of reasons by the way. But the post I was replying to said "bills are over £200pm".