Concerns have been raised after Outfox the Market changed the way it bills direct debit customers.
The supplier said customers will now be charged significantly more in winter than in summer.
A typical customer will pay around 40 per cent more between October and March than they currently do and around 40 per cent less between April and September. This means prices will more than double between summer and winter.
New direct debit charges for a typical customer
In a statement on Facebook, Outfox the Market said: “We have had some feedback from customers concerned that the new ‘winter uplift’ will be their new payment for the next 12 months.
“This is not correct. To be abundantly clear, these payments will be limited to December, January, February and March.
“Your payments will then be reduced to the much lower summer schedule for April, May, June, July, August and September. The winter uplift will then begin again in October 2019.”
The statement said the supplier passes on the “true reflection of the cost of energy” to its customers, suggesting rising wholesale costs have been a factor in the change.
An industry source told Utility Week the company is “probably struggling with cash flow”.
In response Outfox said it was financially sound but in order to continue to provide the prices they do, changes have to come into place.
The supplier has also issued an apology after a number of customers were mistakenly sent an email with incorrect information regarding their direct debit payments, which were “over-inflated” as a result of a 25 per cent increase in their estimated annual consumption.
The company said it remedied the issue before claiming any payments, meaning no customers have been overcharged.
Chief executive Keith Bastian said: “It is regrettable that incorrect information was given to our valued customers and for that we are sorry.
“Outfox the Market has made a real and positive difference to the energy market and we are proud to have helped thousands of customers save large amounts on their energy costs by providing some of the cheapest unit prices in the UK.
“To continue to do this, we need to ensure fairness for all our customers with our billing system. Introducing a winter uplift means customers payments simply reflect their consumption. Payments will drop significantly throughout the summer months to reflect lower usage and overall, we remain one of the best priced suppliers in the country.”