I am in the process of going through this nightmare with Swiss customs at the moment. I shipped my motorcycle riding gear to Switzerland to go on a two-week ride in the Alps, then shipped it back. The shop where I rented the bike (and shipped the gear) HAD to pay almost $400 in duty before Fed Ex would release the packages.
I have successfully convinced the Swiss customs people that they made a mistake, and now they are sending all sorts of forms and paperwork back and forth trying to get me a refund. It's been two months now.
I subsequently learned that I could have avoided this problem if I had addressed it properly.
I had my name in the "from" side, and the name of the shop in the "to" side. What I should have done is had my name in both the "from" and the "to" side, with "c/o motorcycle shop" on the second line. That 'care of' bit helps identify the fact that the goods are not being permanently imported.
If you did that, then they have absolutely no leg to stand on, and they need to be soundly thumped. If, however, you simply addressed the package to a name other than yourself (i.e. your cousin), then there's no way for customs to guess than it's anything other than an importation of goods, for which customs and duty are appropriate. You then have to rely on the care and understanding of a bureaucrat and hope they will agree to waive the charges.
The amount of customs and duty is scandalous however. What sort of declared value did you put on the package?