The only things really that should go "poof" from your inventory is the Beta/Alpha access, and the expanded colors/surname items as those come with your package and can't really stack.
If you're getting charged that bad its best that you go through paypal or your bank for the conversions and you shouldn't switch it to USD with the paypal conversion rates.
I'm unsure how much they can do about the prices showing in your currency because its a US company so they will show in their pricing and most all transaction details go through Xsolla which shows what the conversion would come out to.
At the end of the day, if you're paying in an alternate currency, don't do the conversion, let your bank do the conversion.