It is reversible even if the receipt says it is not. I just had this happen in Ireland on a 05:00 check out. Contact the hotel directly. They have a form from their credit card processor that you can fill out and get a credit. This DCC is a scam as the hotel sets their own conversion rate regardless of the market rate. When you charge in the local currency, you will get the market rate. There is no convenience to bring charged in your home currency!