Customers who have waited too long for energy firm Npower to deal with their complaints are to receive free energy.
About 1,000 customers have been backed by Energy Ombudsman in complaints about Npower, but have waited more than 28 days for problems to be resolved.
Npower will now write off any debt on their accounts and provide free energy until the rulings have been applied.
The agreement came after pressure from the energy regulator, Ofgem, and the ombudsman.
The company will write to those customers affected, many of whom complained about billing errors. Among the major energy firms, Npower received the most complaints in 2014, Ofgem figures have shown.
In March, rival Scottish Power accepted a 12-day sales ban after failing to meet Ofgem’s customer service targets.