Carphone Warehouse has been fined £29.1m by regulators for mis-selling the mobile phone insurance product Geek Squad.
The Financial Conduct Authority (FCA) launched an investigation after whistleblowers alerted the authorities to bad practices.
It found staff were poorly trained to treat customers fairly between 2008 and 2015 – and even urged to recommend the product to people who already had cover through home insurance and other policies.
Carphone Warehouse made Geek Squad sales worth almost £445m over the period.