EE, Britain's largest carrier and the first to offer 4G LTE in the U.K., has been fined £1 million (approx. $1.56 million) for failing to deal with customer complaints properly. The punishment comes after a three-year investigation carried out by industry regulator Ofcom.

"This fine relates to our historic performance regarding complaints handling, collected from 2011 to April 2014," EE explained. "While this is in no way excuses it, it is important to note that we identified issues in our complaints handling and began our programme to tackle these problems head on in 2013, before Ofcom started their investigation."

"We have made considerable improvements since then," the company insists.

Over a near three-year period between July 2011 and April 2014, EE did not send written notifications to customers to explain their right to take a complaint to an alternative dispute resolution (ADR) scheme, Ofcom found.

The ADR scheme allows customers to escalate a complaint eight weeks after it was originally filed with an operator so that an independent body can investigate. But EE did not notify customers of this within an acceptable time scale — and in some cases failed to do so altogether.

Ofcom's most recent figures show that complaints about EE have fallen by around 50% over the last year alone, the carrier says, and it insists it is "working tirelessly" to reduce the number even further and improve the handling of complaints received.