Now comes the first hard evidence that customers have voted with their feet - with 62,000 leaving the energy firm.
An ITV News investigation has revealed that many charities are overpaying on energy bills, but how can the organisations reduce their costs?
An investigation by ITV News has discovered that many charities are being charged too much on their energy bills.
A treasurer at a village hall, which holds events for good causes, told ITV News energy companies should take responsibility on reducing power bills for registered charities.
Val Belton told ITV News: "I think it should be down to the energy companies to raise this question with you particularly when the bill is for Burpham Village Hall - they may think 'maybe that's a registered charity, I'll clarify whether they are'."
An ITV News investigation has shown that many charities are being over charged on their electricity bills.
We asked HMRC how charities can get a refund and whether they accept some charities are missing out on reduced energy bills. Here are their responses:
Does HMRC accept that many charities which are entitled to reduced VAT are missing out?
– HMRC statement
No, HMRC believes that the vast majority who are entitled to receive the reduced rate of VAT and CCL exemption. With millions of supplies made by fuel and power companies, it is not possible for HMRC to determine that every supply is taxed correctly. Ultimately though, the responsibility lies with the individual charity.
How does a charity get a refund for overcharged VAT?
– HMRC statement
If a charity believes it has been charged the wrong rate of VAT on a supply of fuel and power, or that it has been charged CCL, it should contact its supplier and request a refund.
Organisations need to tell energy suppliers they are registered as a charity so the correct tax rates can be applied, Energy UK told ITV News.
The advice comes after an investigation by ITV News showed many charities are overpaying on their energy bills.
– Energy UK statement
When charities register with the Charities Commission it is vital they are told all the benefits to which they are entitled and how to apply.
It is not always obvious from the name that an organisation may be registered as a charity and suppliers can only know if they are told.
Charities should get in touch with their supplier so the appropriate tax rates can be applied. Suppliers want to help where they can and take their responsibility to their customers seriously but are unable to do so if they don’t have all the facts.
Under current HMRC rules companies cannot pay back more than four years of VAT.
Plans to make it a criminal offence to manipulate the energy market will provide a "stronger deterrent" against the practice, Energy Secretary Ed Davey said.
Anyone found guilty of rigging wholesale gas and electricity prices could face up to two years in jail under new proposals.
"Manipulating the energy market is absolutely unacceptable, and these proposals provide a much stronger deterrent - more in line with the approach taken in the financial markets," Mr Davey said.
The Energy Secretary said the government was doing "everything it can to help consumers" with their energy bills.
People found guilty of rigging wholesale gas and electricity prices could face up to two years in prison under new government proposals.
Currently regulators can investigate and fine people who have manipulated the market, but Energy Secretary Ed Davey said he wants to make it a criminal offence.
New laws would make it illegal to fix energy prices at an artificial level or use insider information to buy or sell energy on the wholesale market, with offenders facing a jail term and a criminal record.
The move is aimed at safeguarding consumers and providing a "stronger deterrent" against abuses, the Department of Energy said.
Energy bills are likely to go up in the longer run if Labour come to power, the chief executive of British Gas owner Centrica has told ITV News.
Leader Ed Miliband pledged to freeze energy bills for 20 months if his party wins the general election, but Sam Laidlaw says the plans are likely to scare investors, thereby raising the cost of capital for energy companies and in turn leading to higher bills.
Asked if the plans were already having such an effect, Mr Laidlaw said general "political uncertainty" was raising the cost of capital for energy firms.