Cal. Civil Code § 1788.22

(a) In connection with any covered credit extended to a person under an account: (1) No such person shall attempt to consummate any covered credit transaction thereunder knowing that credit privileges under the account have been terminated or suspended. (2) Each such person shall notify the creditor by telephone, telegraph, letter, or any other reasonable means that an unauthorized use of the account has occurred or may occur as the result of loss or theft of a credit card, or other instrument identifying the account, within a reasonable time after that person’s discovery thereof, and shall reasonably assist the creditor in determining the facts and circumstances relating to any unauthorized use of the account. (b) Each responsibility set forth in subdivision (a) shall apply only if and after the creditor clearly and conspicuously in writing discloses that responsibility to that person.