A total of 1,805 complaints were made last month, which was an increase of 106 per cent from the 872 complaints that were made in December 2012.
Both July and October 2013 had the highest number of energy complaints in the last two years, with the Ombudsman Service receiving 1,867 total complaints about the energy suppliers and networks in each month.
Chief energy Ombudsman Lewis Shand Smith said: “Our complaints figures tell us just how tough things are for consumers.
“We are now receiving more than 300 complaints a week and often these come from people who have been confused by the tariffs on offer.
“Ofgem’s new rules make life simpler and fairer for consumers, which can only be a good thing.”
Energy UK said that “most customers have no problems” with their energy company and agreed with the Ombudsman that Ofgem’s new regulations will improve things for consumers, but did also acknowledge that things can go wrong on occasions.
In a statement the trade association added: “The Ombudsman acknowledges in its statement that new rules brought in following Ofgem’s review of the energy retail market will make things easier and more straight forward for consumers.
“No one wants to see complaints rise but companies use the information to improve the service they provide.”
However, consumer watchdog Which? said that increase in the number of complaints “is yet another indication that the energy market is broken”.
A spokesperson said: “Ofgem’s reforms are a welcome step in the right direction but they just do not go far enough to boost competition and help consumers find the cheapest deals, at a time when millions are struggling with the cost of living.”