California Code, Insurance Code - INS § 11580.010

(a) Any automobile liability insurer that is responsible for coverage for ordinary, reasonable, and necessary medical transportation services provided to an insured, or on behalf of an insured, to a valid claimant is liable for those charges to the person performing those services.  The insurer may discharge this obligation by making payment to the person performing the medical transportation services or to the insured or on behalf of the insured to the claimant.

(b) Any insured or claimant who has received payment, which includes charges for medical transportation services, from an insurer for a loss relating to a vehicle is liable for those charges to the person performing those services.