You should be carefull about confronting a public officer. If she is a bi..ch, she can start a criminal case agaibst you for contraband or for attack to a public officer. Even the case is hilarious, you are going to be under criminal prosecution.
As it was mentioned, you are not a customer, instead you are an adult who has to show up with the proper form filled and the agent didn't lie, you just didn't want/know you have to go with the form.
As far as you are receibing mail from China, they are not stupid, they know that the affidavid that states the box is a present is an obvious lie. So, confronting them is suicidal.
In my experience, it works better to pretend to be humble and ask "how should i do it".