CA Ins Code §10133.66(b)

Reimbursement requests for the overpayment of a claim shall not be made, including requests made pursuant to Section 10123.145 , unless a written request for reimbursement is sent to the provider within 365 days of the date of payment on the overpaid claim. The written notice shall clearly identify the claim, the name of the patient, and the date of service, and shall include a clear explanation of the basis upon which it is believed the amount paid on the claim was in excess of the amount due, including interest and penalties on the claim. The 365-day time limit shall not apply if the overpayment was caused in whole or in part by fraud or misrepresentation on the part of the provider.