EDF Energy is to pay out £3million to benefit “vulnerable customers” after an investigation by regulator Ofgem found the company had breached complaint handling rules.

The inquiry followed an increase of more than 30% in the levels of complaints recorded by the energy company during the mass migration stages of introducing a new IT system in 2011, Ofgem said.

It found that, between May 2011 and January 2012, EDF Energy did not have appropriate procedures in place to properly receive, record and process all customers’ complaints in accordance with complaints handling rules.

Many customers experienced unacceptably high call waiting times, with many deciding to hang up due to the company encountering a number of unexpected technical problems, Ofgem said.

When customers did get through, there was evidence that the supplier failed to record all the required details for the complaints received.

These included the date of receipt, a summary of the complaint and action taken, which could have led to difficulties in tracking progress of consumer complaints.

At times when the new systems were down, complaints were not logged until some time after they were actually received.

The regulator said staff at the energy company took action quickly to rectify the problems and to mitigate the effects on consumers. The company had acknowledged that its customers were caused significant disruption and had publicly apologised for this.

Sarah Harrison, Ofgem’s senior partner with responsibility for enforcement, said: “EDF Energy failed to have sufficiently robust processes in place when they introduced a new IT system and this led to the unacceptable handling of complaints.

“Their commitment to putting things right and paying £3m to the Citizens Advice Energy Best Deal Extra scheme and the Plymouth Citizen Advice Bureau’s Debt Helpline to benefit vulnerable customers is a step in the right direction to rebuilding consumer trust.”

Beatrice Bigois, EDF Energy’s managing director for customers, said: “Despite our best efforts and extensive planning to manage this transition in 2011 without impacting our customers, we recognise that for a period of time the service to our customers was not up to the standards they deserve. We apologise to those customers who were impacted during this period.

“We have cooperated fully with Ofgem and have taken this matter very seriously. The £3m package that we are offering will ensure that thousands of vulnerable customers are provided with free, independent advice on debt, as well as information to help them manage their energy consumption and bills.”