The energy regulator has fined Ovo Energy £8.9m after some customers were overcharged and given inaccurate information.
Ofgem said Ovo Energy had overcharged and undercharged some customers, sending inaccurate annual statements to more than 500,000 people between July 2015 and February 2018 due to IT issues.
The regulator said Ovo Energy had not reported the majority of breaches and was “slow to put things right”.
The fast-growing energy supplier has refunded customers overcharged on prepaid meters and has written off money owed by those billed incorrectly.
Anthony Pygram, director of conduct and enforcement at Ofgem, said: “Our enforcement action sends a strong message that suppliers must get basic services right for all their customers.
“Ovo Energy has accepted the breaches and put processes in place to comply with the rules in future.”
An Ovo Energy spokesperson said the company “holds itself to high standards but we have not always got it right”.
They added: “We accept Ofgem’s findings of issues regarding estimation processes, information formatting and pricing errors.
“We will continue to be guided by the current and future needs of our customers and will keep innovating towards a zero carbon world.”
Ovo Energy was launched in 2009 and by June 2019 it had 1.5 million retail customers.
