It shouldn't really H, but it depends how the Customs declaration was worded. If, for example, it was declared as a personal, medical item, Duty would probably not have been imposed. You can try arguing the point, but, seeing as the Duty has already been applied and registered, it's unlikely you'll succeed. You can, of course, write an official complaint, maybe when you get home, pointing out that the item was neccessary personal medical aid, your own personal property, for your personal and neccessary daily use, and there's a good chance you might get a refund.