My UK Bank just sent me a replacement Mastercard to my address here in Thailand, and a new card reader. Took about two weeks to get here. It is the bank and NOT Mastercard who issue the cards. A debit card is good for up to how much you have in your connected account.
A Thai CREDIT card seems pretty useless to me as you must have as much dosh deposited to cover whatever limit you want, so it is basically the same as a debit card, which is used to spend money which you already have, YOUR money in the bank. A CREDIT card is just that, giving you Credit ie borrowing money which you do not have, which you can either pay off or pay interest on the balance. Would a retailer know whether it was a Debit or Credit Card....I doubt it, they get their money whatever card is used.