Cal. Unemployment Insurance Code § 1036

(a) The director shall give notice, pursuant to Section 1206, to the employer of the correction of any error which the director finds in any statement of account or statement of charges. Except in the case where fraud, intent to evade, misrepresentation, or willful nondisclosure is found, the notice of correction shall be issued prior to the expiration of the rating period to which a statement relates. (b) Any additional amount of contributions resulting from an increased contribution rate caused by the correction of any error that the director finds in any statement of reserve account or statement of charges shall be assessed within 180 days from the postmarked date of the notice of correction. These assessments shall be issued in accordance with Article 8 (commencing with Section 1126). However, these assessments shall become final on the last day of the calendar month following the calendar quarter in which the assessment is issued. (c) Any overpaid amount of contributions resulting from a reduced rate caused by the correction of an error that the director finds on any statement of reserve account or statement of charges shall be refunded within 180 days of the postmarked date of the notice of correction. These refunds shall be issued in accordance with Article 9 (commencing with Section 1176).