Energy supplier Toto Energy has become the latest small utility firm to cease trading.
The firm's 134,000 domestic customers will be transferred to a different supplier by regulator Ofgem. It is the seventh supplier to go bust this year.
Customers are advised not to change energy supplier and wait until their new supplier contacts them.
Toto took over customers of defunct Solarplicity just three months ago.
uSwitch.com energy expert Cordelia Samson said: “Toto are the seventh energy company to go bust this year, hot on the heels of Ofgem’s announcement about toughening up the rules for existing providers, to minimise the risk of more of them going out of business.
“This latest supplier failure must raise serious questions for the regulator, which allowed it to acquire over 40,000 customers from another now-defunct energy company only three months ago."
She added: “Toto were known to be struggling with customer service and running their operations efficiently. They also missed making their payments for renewable energy this year. While they had made improvements, clearly these weren’t enough to keep them afloat.
“Households affected by this news should now wait for a new supplier to be appointed by Ofgem. In the meantime, their energy supplies and credit balances will be protected, and they should take a meter reading ready for when the new supplier contacts them.”
Philippa Pickford, Ofgem’s director for future retail markets, said: “Toto Energy customers do not need to worry, as under our safety net we’ll make sure your energy supplies are secure and customers’ credit balances are protected.
“Ofgem will now choose a new supplier for you and whilst we’re doing this our advice is to ‘sit tight’ and don’t switch. You can rely on your energy supply as normal. We will update you when we have chosen a new supplier, who will then get in touch about your new tariff.”