In most small claims actions where liability for the claim is denied, the defendnat answers the complaint denying the claim and asserting as many affirmative defenses to the complaint as he or she can.In your instance, you might consider asserting various defenses including, but not limited to the fact that your insurance carrier is responsible for the medical bill.Another tactic you might wish to consider is that when you file your answer, you file a cross complaint against your insurance carrier claiming that it is responsible ultimately for the monies claimed for the $400.00 medical bill at issue. You would then need to serve your insurance carrier with the summons and your cross complaint for this dispute.Good luck.