A congressional probe has found private health insurers have forced consumers to pay billions of dollars in medical costs that the insurers should have paid. In a new report, the Senate Commerce Committee says insurers have relied on faulty databases that have led to underpaying on millions of valid claims for out-of-network medical care. Patients have been forced to make up the difference. The report says the databases’ errors were easily disguised because insurers have failed to properly inform consumers on how they calculate charges for out-of-network costs. The databases are owned by a company named Ingenix. The firm has a financial incentive to underpay consumers: it’s a subsidiary of UnitedHealth Group, one of the nation’s largest private insurers. In addition to UnitedHealth, at least seventeen other leading insurance companies have relied on Ingenix’s data.