Consumer expert Martin Lewis has urged Brits to check their monthly energy bills after thousands have reported their costs doubling - despite being on price-capped tariffs.
According to research done by Lewis' company, Money Saving Expert, 30% of British Gas, Octopus Energy and Shell Energy customers who were in credit and on price-capped tariffs have seen their prices increase by two-fold.
This is despite the price cap raise being fixed at half that - 54% - as Brits face a cost of living crisis.
More than 41,000 people were quizzed on their energy costs, with 25% across all firms reporting their direct debits have at least doubled.
Lewis said: "Those coming off cheap fixes, moving to expensive fixes, or who are in energy debt would expect to see their direct debit rise by more than the already hideous 54% increase in the energy price cap.
"So to test what's really happening, we analysed responses only from those in credit who were on, and remain on, a price-capped tariff – as they should only be seeing rises in line with the price cap – roughly 45% to 65%.
"Yet even then, on average, many report higher rises, and a quarter say they were told to pay double what they were paying previously. That smells wrong to me.
"While a higher direct debit doesn't mean you pay for more energy than you use, as any overpayments are ultimately due to be repaid, it does mean far too much cash flowing from accounts now, which is often a nightmare amid the cost of living crisis."
Many have said they have not challenged this rise, as they didn't realise they could.
But there are ways to try and reduce the amount your energy is costing.
Watch: Shoppers 'put brakes' on spending as consumer confidence dips
How can you bring your tariff back down?
Lewis added that under firms' licence conditions you have a right to a fair direct debit, meaning that if you're in credit and have been on a price-capped for more than six months and your direct debit has skyrocketed there is something you can do.
He recommends submitting an up-to-date meter reading before speaking to your supplier and politely asking them to justify the rise.
If they are unable to - then ask it to be lower.
If they refuse - make a formal complaint and take it to the Energy Ombudsman.
The government has come under increasing pressure to tackle the growing crisis, but has so far opposed calls for windfall tax on energy firms.
What is a windfall tax?
A windfall tax is a one-off tax brought in by a government on a single company or group of companies to target firms which have benefitted from something they were not responsible for.
For example, companies which specialise in extracting oil and gas out of the ground are getting more money because of the demand for it in the aftermath of COVID-19, and fears over the Russian invasion of Ukraine.
Chancellor Rishi Sunak held firm in his opposition to a windfall tax on Monday, arguing that it would “deter investment at a time we need it most – not least in renewable energy”.
But Downing Street has not ruled out the possibility that energy bills could rise by nearly £1,000 for most customers when the regulator reviews the price cap in the autumn.
Bills for the average household whose tariff is tied to the energy price cap rose to £1,971 on April 1 after the price of gas soared over previous months.
It forced the Government to promise the £200 rebate on energy bills from October and also knock £150 off council tax for many households.
But many campaigners have warned that this will not be enough, especially next winter if the price cap goes up again, which is widely expected.
ScottishPower believes this might go to £2,900 on October 1.