Cal. Rev. & Tax. Code § 9151
If the department determines that any amount not required to be paid under this part has been paid by any person, the department shall set forth that fact in its records and certify the amount paid in excess of the amount legally due and the person by whom the excess was paid to the department or from whom it was collected. The excess amount paid or collected shall be credited on any amounts then due and payable from the person from whom the excess amount was collected or by whom it was paid under this part, and the balance shall either be refunded to the person, or the person's successors, administrators, executors, or assigns, or, if authorized by the department, deducted by the person from any amounts to become due from that person under this part.
Any overpayment of the tax by a user to a vendor who is required to collect the tax and who gives the user a receipt therefor pursuant to Section 8732 shall be credited or refunded by the state to the user.
For any amount exceeding fifty thousand dollars ($50,000), the department's determination under this section shall be available as a public record for at least 10 days after the effective date of the determination.
Ca. Rev. and Tax. Code § 9151