California regulators have moved to stop Prime Healthcare Services Inc. from billing privately insured patients for unpaid medical services received at its facilities. The Department of Managed Health Care has filed a lawsuit seeking to bar Prime Healthcare from billing insured patients for unpaid medical bills that the hospital chain contends it is owed from insurers and is seeking from patients as a last resort. Prime Healthcare representatives said they believed that the hospital operator was legally allowed to send the bills to patients and that it wouldn't have to do that if insurers paid their portion of the medical bills.