Customers have been paying too much for their electricity for seven years because regulator Ofgem set the bar too low for networks, the spending watchdog has said.
Energy customers are still struggling to get accurate bills despite it being "the very least they should expect", according to Citizens Advice.
Energy customers have been warned to look further than "attention-grabbing" low tariffs following the failure of 13 firms since November.
Consumers should be compensated after being overcharged for their utilities by more than £20 billion due to regulator errors, Citizens Advice says.
A consumer group has called on Ofgem to set out how it will better support vulnerable energy customers who fall behind on their bills.
Citizens Advice has called for tighter licensing rules for new energy companies after finding an increasing number are delivering poor customer service.
The increasing cost of the smart meter rollout to households could become "potentially even greater" amid a "real information gap", a consumer group has warned MPs.
Households have fallen behind on essential bills such as council tax and utilities by an estimated £18.9 billion, according to Citizens Advice.
Around 140,000 British households have been left without gas or electricity in the last year because they cannot afford to top up their prepayment energy meter, a charity has found.
A new ranking of energy company customer service has raised “serious questions” about licensing rules for smaller firms, Citizens Advice has warned.
Energy price cap plans must be introduced urgently to stop millions of loyal and vulnerable customers being ripped off, a powerful committee has told the Government.
Consumers have made nearly 20 times as many complaints per 100,000 customers about some energy companies as they have about the best-performing suppliers, according to Citizens Advice.