Ofcom imposed a £1 million fine on UK operator EE over its failure to comply with regulator rules on handling customer complaints.

The fine, which is one of the largest handed out by the UK watchdog, is further evidence of the hard line adopted by new Ofcom chief executive Sharon White, who vowed to address poor customer service amongst operators when taking over in April.

In a statement, Ofcom said that it found EE guilty of not providing “certain customers with accurate or adequate information about their right to take their complaint to an Alternative Dispute Resolution (ADR) scheme”, during a three year period dating back to July 2011.

EE, which is in the process of being acquired by BT, should have informed its customers in writing about their right to redirect complaints to the independent body within two months, which it did not, according to Ofcom.

The operator further failed to state the information in its customer complaints code, and did not notify customers on paper bills of their right to take any complaints to an ADR for free.

“It’s vital that customers can access all the information they need when they’re pursuing a complaint,” said Claudio Pollack, Ofcom’s consumer and content group director. “Ofcom imposes strict rules on how providers handle complaints and treats any breach of these rules very seriously.”

According to Ofcom, EE has now amended its customer complaints code to include the information on paper bills.

The Financial Times reports an EE spokesman responded to say the company had made “considerable improvements” regarding complaints since Ofcom began its investigation in 2013.

Sharon White assumed her new position earlier this year, and declared her intent to address operator customer service in her first speech as Ofcom’s new head in June.

At the time, White said people should have the right to find an alternative if their operator fails to deliver. “People legitimately expect and demand more from their communications than ever before. Service failure, where once an inconvenience, can today be very costly for people in terms of loss of business, disrupted access to public service or social isolation.”

EE has 20 days to pay the financial penalty, before it is passed on to the UK treasury.