More energy customers (60%) contact Citizens Advice about bill errors than any other issue related to their gas and electricity supply.

They are also the most common gripe by customers of three of the bottom five suppliers – Ecotricity, Outfox The Market, Green Star – according to the charity’s latest energy customer service ratings.

Nearly one in five (17%) energy customers contacting Citizens Advice were unhappy about how energy complaints were handled, and 12% complained about phone waiting times.

Based on customer feedback, Nabuh Energy comes bottom for the third quarter while Breeze Energy tops the table for the second time.

‘Big Six’ energy suppliers EDF and E.ON made it into the top five while Toto Energy which went out of business in October, was previously in 37^th position.

In the last two years, 14 domestic suppliers have gone out of business.

In one case seen by the charity, Gean was paying Green Star Energy by direct debit, topping up amounts when they used more than expected. But when she wanted to switch, she was told they owed £900. Gean and her husband repeatedly asked for a breakdown of the bill but received no reply.

Her husband was diagnosed with cancer and to reduce the stress, they used savings to cover the amount. However they continued to receive demands for payment and after her husband died, she again told them to stop. She contacted Citizens Advice who explained the situation to Green Star Energy and the letters finally stopped.

Gillian Guy, chief executive of Citizens Advice, said every energy firm should be able to provide customers with an accurate bill.

“The inability of some suppliers to get this right causes a great deal of unnecessary stress for customers.

“Some of the difficulties experienced by people who come to us for help are a legacy of an under-regulated market. Too many under-prepared companies were allowed to set up as energy suppliers.

“We’d like to see Ofgem making basic customer service such as accurate billing a top priority, and step in sooner when energy companies don’t meet decent standards of customer service,” she said.

YourMoney.com has contacted Green Star Energy for a response. We’ll update this story once we hear back.