lI won't "name and shame" the restaurant: dinner was wonderful and I am not accusing them of deliberately attempting to rip us off. It seems more likely that the cashier made a mistake (or was on autopilot and selected the option most often chosen by foreigners?).
No need to disclose the merchant (restaurant) but can you disclose the acquirer (bank/processor)? I wonder is it Global Payments (I have some history getting involuntarily opted into DCC with them in Taiwan) or another acquirer.
Generally in Taiwan the acquirer is disclosed on the card slip.