They shove it to you, legally, you can shove it right back. Give at'er, you ain't got much to lose. If you give in to "they're customs, they can do whatever the fuck they want", you deserve to lose your money. Fight for your rights, or lay back and let democracy erode (this is the big picture I'm getting at).
Try to reason with them, but as a licensed importer, I can tell you outright that they have this feeling that they think they're almighty and no one can touch them: every person that fights back
(with a valid, legal, and legitimate reason, of course), is a little nick in that huge egotistic attitude they have.
You can pursue just about any legal entity, really: it usually just boils down to how much time you're willing to waste (and in some cases, money).
Opea's got the right idea going on there, but I'm almost positive they will play the "bitch" position, and say "we're never wrong", as they always do. So instead of one letter, it will be two, or three. This is what pisses me off about customs: they rarely ever
directly admit to making a mistake.
If some people are wondering why I'm so bitter to customs, it's because my first business order went through under my personal name: this is legally permissible, I was importing stock in preparation to my grand opening, but had not begun transactions. However, mid-way through shipping, I changed over to my new, (then newly registered) business name, which, although done through UPS, I also relayed th new info to customs. Customs had a hissy fit about it, and nearly seized two thousand dollars worth of radio stuff, without a valid claim. It took three weeks to release my shipment, but man oh man, that feeling of getting the shipment and giving them the middle-finger salute was almost worth it.