An industry watchdog had found all of Western Australia's energy retailers have overcharged hundreds of customers in the past two years.

WA Government-owned Synergy was the first – and the only one to be dealt a breach notice by the regulator for its $40 million in overpayments.

But now all seven of WA's energy retailers have been found to have overcharged customers.

There's been $213,000 of extra cash taken from closed Horizon Power accounts, $175,000 from Kleenheat customers and $155,000 from Alinta Energy customers.

WA Premier Roger Cook labelled it "very serious" and said the government was "extremely angry" over the situation.

"You can have confidence that we will make sure that when mistakes are identified that we will rectify the situation and insist on it," Cook said.

The Eco

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