If you can, make sure the vendor is shipping via their national post system (i.e. US Post, UK Royal Mail, etc) and hence via the Swiss Post instead of using a courier company. The latter make sure they add a hefty Zollabfertigung, tax and other charges at the border. About 5 years ago I had a similar experience with DHL as cobenz, including the futile phone call.

Note that the Swiss Post are raising their customs prices from 1st October. Details are here, with PDF.