Nearly a fifth of households have been billed incorrectly in the last two years by their energy providers, new research has revealed.
And 11% received the wrong bill on more than one occasion, according to comparison website uSwitch.
Its research also revealed that 39% of billpayers found themselves owing money to their supplier following a difference between an estimated and ‘actual' bill, with the average amount owed £146.
A further 14% had to find between £200 and £400 to make up the shortfall, and 7% more than £400.
Consumers are also having to wait longer for billing issues to be resolved, with it taking almost two months for an issue to be dealt with compared to just one, according to last year's research.
Only 39% of complaints are being resolved in a week compared to 42% a year ago, and only 11% are being sorted out in 24 hours - down from 16% last year.
Billpayers are becoming more proactive, however, with 80% of households providing their energy supplier with their own meter reading in the past six months – up 3% on last year's figure.
Ann Robinson, director of consumer policy at uSwitch, said: "Consumers are typically paying over £100 a month for gas and electric, so the fact that they cannot rely on the accuracy of their bills is simply unacceptable," she said.
"With energy bills accounting for the largest chunk of household expenditure after rent and mortgage payments, billing blunders can leave consumers feeling frustrated, susceptible and out of pocket.
"There is a toxic link between estimated bills, inaccuracy and debt, which has to be broken. Estimated bills should come with a health warning and with a very simple message and advice about them.
"If a bill is estimated then the customer should be encouraged to get in touch with a correct reading so that an updated and accurate bill can be sent."
Overall, energy suppliers came behind only HMRC according to the switching website's most inaccurate list.