Energy giant Npower is Britain's most complained-about major power supplier, according to new figures.
The German-owned firm, which imposed the highest price hike last winter, received 10 times as many complaints as its best performing rival.
Data from the Citizens Advice Bureau showed that between October and December last year, Npower was inundated with 306 complaints for every 100,000 customers.
That is three times as many as the second worst performing supplier, Scottish Power, which attracted 100.5 complaints per 100,000 customers.
The revelation is the latest in a series of blows for the firm, which was heavily criticised when it imposed inflation-busting price rises of 10.4% last October.
The firm's new billing system has been blamed for causing widespread frustration and anger among its customers, who have complained of being stung with inaccurate charges.
And the problems have taken their toll on the supplier's ratings, as its complaint figures have soared by 300% from January 2012 until December 2013 - from just over 100 to more than 300 for every 100,000 customers.
Citizens Advice chief executive Gillian Guy said: "Things are getting worse not better for Npower customers.
"It is unacceptable that Npower has not yet sorted out the serious failings in its billing systems and customer service which are causing so many complaints and serious problems for its customers.
"For well over a year now some Npower customers have been finding their finances thrown into chaos.
Some are not receiving bills and others are ending up in debt because their direct debit was cancelled.
"Citizens Advice has asked Npower to make sure people affected get any appropriate compensation.
"Time and time again energy suppliers are letting customers down. People will not feel able to trust energy suppliers again if firms cannot get their house in order and deliver decent customer service."
The survey shows that Npower, which has 5.9 million customers in the UK, has languished at the bottom of the energy complaints league table since the end of 2012.
Among the top gripes were bills arriving late, payments being stopped and new accounts not being set up.
Margaret Lynch, chief executive of Citizens Advice Scotland, warned that energy price rises have left many homes having to make the impossible choice of heating their homes or putting food on the table.
She said: "Fuel poverty is a particular issue in Scotland, due to the colder climate and the poor quality of housing stock in many rural areas.
"The CAB service sees so many people now who are simply unable to pay their bills. Many have to choose between heating their home and putting food on the table. All of the fuel companies need to do more to put consumers first."
Roger Hattam, director of domestic retail business for NPower insisted the firm is tackling its customer service problems.
He said: "We wrote to all our customers during this period last year apologising for the impact on them of issues we have had with the implementation of our new billing system.
"We are making good progress in dealing with the root causes of this, but remain totally committed to resolving any problems this has created for our customers."
Energy firm EDF was the third lowest scoring of the Big Six suppliers, receiving 62 complaints for every 100,000 customers, while E.ON came fourth with 55.8.
Scottish and Southern Energy was the best performing of the firms attracting 31.5 complaints per 100,000 customers, while British Gas came second receiving 53.7 complaints.
Citizens Advice Bureau urged homes who encounter problems with their energy suppliers to complain immediately and to set aside money if you are expecting a bill.
The debt charity said households which have spent time trying to sort out bungled energy bills should ask for compensation from their suppliers.