(CBS SF) – One in three Americans with private health insurance has been hit with a surprise medical bill, according to a new survey by Consumers Union. The study of 2,200 individuals also found consumers overall are confused when it comes to how to fight a surprise bill.

Among the surprises: bills that were for higher amounts than customer’s expected, bills for out-of-network services that customers believed were in-network, and bills from doctors they did not expect would send them a bill.

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Betsy Imholz of Consumers Union says few people who receive surprise bills ever file a complaint with a state agency. “Nobody got that far at all, in fact, almost zero,” Imholz told KPIX 5 ConsumerWatch.

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Earlier this year, California’s Insurance Commissioner imposed two emergency regulations that now require hospitals to disclose if any part of a patient’s treatment will be out-of-network. It also requires insurers to pay some out-of-network costs when an in-network provider cannot be found in a “timely manner.”

But, Imholz and the State’s Department of Insurance say without complaints, state regulators can’t hold insurers or providers accountable.

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Consumers Union has set up a tool that directs consumers to the appropriate agency where they can file a billing complaint.