Cal. Civil Code § 1788.11

No debt collector shall collect or attempt to collect a covered debt by means of the following practices: (a) Using obscene or profane language. (b) Placing a telephone call without disclosing the caller’s identity, provided that an employee of a licensed collection agency may identify oneself by using their registered alias name if they correctly identify the agency that they represent. A debt collector shall provide its California debt collector license number, if applicable, upon the consumer’s request. (c) Causing expense to any person for long distance telephone calls, telegram fees, or charges for other similar communications, by misrepresenting to the person the purpose of the telephone call, telegram or similar communication. (d) Causing a telephone to ring repeatedly or continuously to annoy the person called. (e) Communicating, by telephone or in person, with the debtor with such frequency as to be unreasonable, and to constitute harassment of the debtor under the circumstances. (f) Sending written or digital communication to the person that does not display the California license number of the collector, if applicable, in at least 12-point type.