MetLife will pay at least $50,000 in penalties and refund an undetermined amount of money to customers to settle allegations it imposed costly surcharges on Massachusetts drivers who were found not at fault in auto accidents.

State attorney general Martha Coakley said Tuesday that some customers of Metropolitan Property & Casualty Insurance Company—a unit of MetLife—who filed accident claims with the company were improperly penalized even after a state appeals board had ruled they were not responsible for causing the crashes.

Under Massachusetts law, a driver assessed a surcharge by an insurance company because they are deemed at-fault in an accident can appeal the insurer’s decision to the state. If the appeals board vacates the surcharge, the company is required to halt the extra charges and refund any penalty money already collected.

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MetLife said it is working with the attorney general’s office to make sure customers who were incorrectly charged surcharges “receive the appropriate refunds.”

Coakley’s office said it has also started investigating whether other auto insurance companies in Massachusetts have similarly violated the law.

State officials said they began looking into the issue after receiving a complaint from a MetLife customer.

“This is another example of an auto insurance rating problem that our office discovered as a result of a consumer complaint,” Coakley said in a statement. “While we are troubled that these overcharges occurred, we are pleased that we were able to stop this unlawful practice and protect consumers.”

Charles DiPompo, the customer who contacted the attorney general, said he was hit with a surcharge after he was involved in a fender bender in 2008. But MetLife kept charging him an extra $30 a month for about a year after he persuaded the state that he wasn’t to blame for the accident.

“I felt they weren’t listening to me,” said DiPompo, 64, of Foxborough. “I felt they were giving me the run-around and not treating me fairly.”

As part of the settlement, MetLife agreed to an audit that will determine how many customers were affected, calculate the amount of restitution owed them, and prevent such overcharges from happening in the future. The company also agreed to pay the state at least $50,000.

MetLife was the seventh largest auto insurer in the state in 2010, according to the most recent data available from the Division of Insurance. The company’s parent, MetLife Inc. of New York, is a major provider of insurance, annuities and employee benefits programs. It has about 90 million customers nationwide.

In September, MetLife agreed to pay $395,000 in restitution after wrongfully terminating 2,600 auto policies in Massachusetts.

The state said MetLife auto insurance customers who believe they were incorrectly assessed accident surcharges should contact the attorney general’s insurance and financial services division at 888-830-6277.