The charity found households signed up to some of the worst performing energy firms face problems with incorrect bills, aggressive debt collection and faulty meters. As a result, Citizens Advice is urging households to compare companies’ customer service performance, as well as prices, when choosing an energy provider.

The Citizens Advice star rating tables assess a wide range of customer service indicators, including accuracy of bills, call waiting times, and complaint handling.

The tables for April to June 2019 found the top energy firms were: Breeze, SSE, Igloo, So Energy and Engie. These all scored at least four out of five for customer service.

At the other end of the scale, the worst firms were: Ecotricity, Green Star, Toto, Utilita, and Nabuh Energy. These firms all scored between 1.9 and 2.2 out of five for customer service.

The scores show there is a big gap between the best and worst energy firms when it comes to how they treat their customers.

Customers of firms at the bottom of the rankings face issues with inaccurate bills, incorrect and late final bills, or not receiving any bills at all. Other issues include debt and disconnection issues, and aggressive debt collection practices.

Many customers also have issues with meters, such as meters being incorrectly registered to a property or problems with credit refunds on prepayment meters.

Thirteen domestic energy supply companies have gone out of business since November 2018. Six suppliers (Economy, Our Power, Brilliant, Cardiff, Solarplicity and Eversmart have failed so far this year – affecting more than 300,000 people.

Gillian Guy, chief executive of Citizens Advice, said: “There is still a big gap between those firms who provide an excellent service to consumers, and those who are letting people down. Attention-grabbing low tariffs can be a good deal, but we recommend looking deeper than just the headline price when shopping around for the best energy deals.

“We’ve seen six energy suppliers go bust this year. In our experience, when a company is struggling, customer service is often the first thing to suffer.“