Energy supplier Toto has ceased trading, becoming the 16th smaller provider to go bust since the start of last year.
The company, which had 134,000 domestic customers, had bought 43,000 of those from another failing supplier – Solarplicity – in July.
Energy regulator Ofgem said it did not have the power to step in at the time of that handover.
The regulator said Toto customers should take a meter reading.
But it stressed that their energy supply will not be cut off. They should not switch away but wait for another supplier to be appointed to take up their account.