Why should we pay excess duties for Fedex's errors?

Appalling customer service from Fedex South Africa. Apparently, because someone at Fedex used the wrong code for clearance (despite the supplier's invoice being correct and stipulating contents), I must now pay excess duties. Additionally Fedex has charged me VAT on the shipping when the suppliers invoice CLEARLY showed the breakdown of charges for shipping and the contents. They cannot even be bothered to acknowledge their error or apologize. Fedex should not be allowed to bully or partonize customers into paying duties and VAT which has been incorrectly calculated. What a disappointment when you pay R850 for shipping freight and then get this type of customer service.