Yeah, you have to watch those variable exchange rates. Though, looking at their online shop, I saw nothing that said the price charge would be subject to current exchange rate against the local currency. It just lists prices in US Dollars and no statement as estimated exhange conversion, so they should charge you the listed US$ price. Therefore no currency conversion by the credit card company.
Contact Elbox and your card company. All the credit cards I know of are used globally.
