Need to verify the terms of the settlement included any unpaid bills and your attorney, the doctor or you need to contact the insurance company. In Illinois you can file a petition to enforce the settlement and request penalties for the failure to pay bills covered by the settlement. I expect CA has similiar rules.
Did you settle your case with continuing medical care (Stip and Award) or without continuing medical care (Compromise and Release)? Are the doctors billing you for treatment before or after the settlement? Are they billing you for treatment related to the work injury or for something else?
If they are billing for work injury related treatment and treatment from before the settlement, you might want to direct them to labor code 3751(b) that prohibits them from billing you and makes it a felony. Your lawyer should have a form letter for this type of situation. Make an office appointment to see him. Take a copy of the bill with you.