A "myriad" of problems with energy billing is causing debt and misery for consumers, a watchdog has said.
Inaccurate billing causes misery for consumers, says Energywatch
Energywatch received 40,000 complaints last year, including gripes about firms failing to deliver bills for months and sometimes years.
The watchdog has asked regulator Ofgem to investigate the issue, in what is the first energy "super complaint".
The Energy Retail Association (Era), representing suppliers, said it was surprised by the move.
Under the Enterprise Act 2002, consumer bodies, such as Energywatch, can use a super complaint to bring particular issues to the attention of regulators.
Ofgem confirmed it had received the complaint and said it would respond within 90 days.
As part of the process, Ofgem said it would also be inviting views from energy suppliers.
Energywatch said it had become increasingly fed up with "incompetence" over billing and said suppliers had consistently failed to address the issue.
It said customers were being sent bills which were not their own, or which were too high. Despite the mistakes, customers were being threatened with being cut off for not paying.
In one area, the consumer group said that more than a hundred pensioners on an estate went unbilled for at least six months.
"Billing is the single biggest problem consumers have with energy suppliers," said Energywatch's chief executive Allan Asher.
"Industry has consistently resisted any reform which is why we hope Ofgem will force through a radical overhaul of the billing process."
But Era said complaints were low and had fallen. It said complaints to Energywatch about billing over the last year had fallen by 17%.
"It is baffling that Energywatch has chosen to lodge a super complaint... especially since last month we announced a programme of industry-wide work to tackle billing issues," said Duncan Sedgwick, chief executive of Era.