A British energy supplier is to stump up 12 million pounds (20 million U.S. dollars) compensation for customers after energy watchdog found it mis-sold energy package to customers. The leading power and gas company, E.ON UK, apologized to its customers on Friday, promising not to repeat their misconducts. The company made this decision after the Office of Gas and Electricity Markets (Ofgem), the regulator of the gas and electricity industries in Britain, found it had broken energy sales rules between June 2012 and December 2013 when a large number of customers were mis-sold to by the company. But no evidence showed the mis-selling was done deliberately. The regulator said investigation found the company failed to properly train and monitor its own staff and a third party it employed, leading to incorrect information being provided to customers on the face-to-face sales and telesales. "We are really sorry and want to make it absolutely clear that we're putting this right," said Tony Cocker, chief executive of E.ON UK. The company said about 333,000 vulnerable customers, including pensioners, disabled and low income families, will individually receive a payment of around 35 pounds, making a total of 12 million pounds. About 465,000 customers will receive a letter to identify whether they were mis-sold to, and they will receive payment if they are confirmed victims of mis-selling. Customers with concerns can also contact the company through a dedicated hotline, the company said. In 2012, the company was fined 1.7 million pounds by Ofgem after it overcharged about 100,000 customers on their energy bills.