Energy regulator Ofgem has accused npower of producing a "misleading" report about the cost of producing gas and electricity.
The firm had argued that rising costs of transporting energy meant they could do little to control the prices charged to consumers.
Npower had released documents claiming those transportation costs would increase by around 20% by 2020, but Ofgem said the data was "incorrect and misleading".
More top news
The public love him but The X Factor judges seem shocked the Essex crooner has lasted three weeks on the live shows.
Rumours are swirling comedian Russell Brand is considering running for Boris Johnson's job.
Scotland could see heavy rain and localised flooding but for the rest of us it should be a dry and mild Sunday.