As part of the energy ‘Guaranteed Standards’, suppliers are required to compensate customers when agents mis-schedule appointments.

But in 2014, Big Six provider E.ON approached the energy regulator, Ofgem, to report it had missed some appointments and then failed to compensate customers.

At the time, suppliers were required to pay a rate of £20-£22 (depending on whether it was for gas or electricity) for a missed appointment and if it failed to pay the amount within 10 days, the amount would double to £40-£44.

Ofgem found that E.ON missed 35,000 appointments and while it’s managed to trace some 24,000 affected to repay them a total of £1.2m, there are outstanding customers who can’t be tracked down.

As a result, it will also pay £1.9m to charity to help those in need, including service personnel through National Energy Action’s ‘Help for Heroes’ scheme.

Ofgem’s chief executive, Dermot Nolan, said: “E.ON fell well short of the high standards we expect for consumers when it missed appointments and then failed to compensate customers.

“It’s crucial that suppliers provide their customers with a fast and effective service, and make amends when things go wrong.”

Under the ‘Guaranteed Standards’, customers facing a missed appointment now receive £30 compensation.