Scottish Power has been named and shamed as the most complained about big energy supplier by Citizens Advice. The charity said complaints flooded in between January and March at a rate 1,154.6 per 100,000 customers. Scottish Power was the most complained about member of the Big Six in each of the past four quarters. SSE emerged as the least complained about big supplier between January and March, with 55.1 complaints per 100,000 customers. The total number of complaints about the Big Six energy companies rose during the period to an average of 271 per 100,000 customers, up from 258 between October and December 2014.Compare energy prices and switch provider Lack of improvementCitizens Advice was dismayed at "the lack of improvement" in the figures, "despite a number of firms receiving sanctions from the regulator Ofgem for poor customer service in 2014-15". Previous research from the charity found that the majority of complaints were to do with billing issues. At the end of last year, Scottish Power became the worst performing supplier based on the number of complaints received after introducing a new billing system which caused problems for many customers. Gillian Guy, chief executive of Citizens Advice, said: "Energy firms have no excuse for continued poor service. "The majority of complaints from customers are about their bills, from large back bills to incorrect bills, or even no bill at all. With billing a basic part of the service energy firms provide, it should be the simplest thing to get right." If you are experiencing difficulties with your energy provider, Citizens Advice gives the following advice: Complain to your energy supplier as soon as you experience a problem. If you have not received a bill but are expecting one, try to put money aside so you are able to pay when you do eventually get the bill. Energy companies are only allowed to back bill for energy you used in the last 12 months, anything older than that should be written-off where the supplier is at fault. Ask for some sort of compensation for the time you spent on trying to sort out problems and the financial impact of late billing, for example reduce the balance of the bill and cover the cost of phone calls. If you are struggling to resolve your complaint you can raise it with the energy ombudsman on 0330 440 1624.