More than 5.5 million customers of the Big Six complained about the service they received in 2013, new figures have revealed.
Top of the hall of shame was Npower with 1,383,650 complaints, followed by EDF with 1,240,005 and British Gas, who recorded 1,235,550.
Eon received 929,230 complaints, while SSE and Scottish Power dealt with 482,582 and 308,648 respectively, bringing the final total to 5,579,665.
Tellingly, the most complaints - 1,492,065 - were received in the last quarter of 2013 when all six firms announced price hikes. The type of complaints ranged from bills and customer service issues to metering and payment problems.
Green energy company Ecotricity received only 500 complaints last year, the lowest number of complaints recorded against a company. The figure means it received just 1.74 complaints per 1,000 customers across 2013.
Npower had on average 63.56 complaints per 1,000 account holders, EDF received 56.51 and Eon 31.62. This was followed by British Gas, which received 19.96 complaints per 1,000 customers, SSE with 14.8 and Scottish Power with 14.6.
Ann Robinson, director of consumer policy at uSwitch.com, said: "This is why it's so important that we get competition working in the energy industry.
"Competition is the beating heart of a healthy market leading to consumers benefitting from fairer pricing, better customer service and greater efficiency. But we have a long way to go. Trust in energy suppliers has hit rock-bottom which has led to disenchanted consumers who are reluctant to engage. But the reality is that we need them to engage as this will start driving suppliers to up their game."
Today Which? has launched a new campaign calling for the government, energy companies and regulators to reform the energy market with 'six fixes'. These are:
FIX NO.1. Increase competition
FIX NO.2. Transparent trading
FIX NO.3. People power
FIX NO.4. Cost control
FIX NO.5. Customer trust
FIX NO.6. Warmer homes
Which? is also calling for a full competition inquiry into the energy market to look at whether it is working for consumers. The Big Six account for 97% of the entire market in the UK.
Executive director Richard Lloyd said: "Millions of people are unhappy with the service they receive from the suppliers which, combined with low levels of trust is yet more evidence that more must be done to fix the broken energy market.
"Next month we want the regulators to refer the energy market to the Competition and Markets Authority and launch a full scale inquiry. This is the first and most important step towards a more radical reform of the energy market, giving hard-pressed consumers the
confidence that they are paying a fair price."
Earlier this week energy secretary Ed Davey said the Big Six should be investigated over their gas profits and could be broken-up if they are found to be ripping-off customers.