If the minor served you, you can attempt to avoid service via motion to quash. You should absolutely inform the court, via motion to quash or other appropriate motion, as this is very bad conduct and should not continue.
Best of luck to you.
This response is intended to be a general statement of law, should not be relied upon as legal advice and does not create an attorney/client relationship.
You can notify the court in a specific action. You can notify the attorney that his letter head is being used without his permission. What the minor is doing is potentially against the law because most POS's are signed under penalty of perjury.
Civil Code SECTION 414.10 states:
414.10. A summons may be served by any person who is at least 18
years of age and not a party to the action.
This is a general discussion of legal principles by a California lawyer and does not create an attorney/client relationship. This is not intended to be legal advice in your specific case. It's impossible to give detailed, accurate advice based on a few sentences on a website. You should always seek advice from an attorney licensed in your jurisdiction who can give you an informed opinion after reviewing all of the relevant information in your case.