maybe, there are so many cards like this all of them free of charge if you need more than 250punds you can get another card but I guess for summer holidays in Thailand 250 pounds is more than enough for most of people
Get revolut or similar card, then you pay only 220 Bath for transaction and get the best possible exchange rate. 7eleven, big supermarkets and restaurant chain accept cards.
In the reason you may write "extension due to covid-19" I think they usually give you document where you might check the box "my embassy doesn't issue letters of support" or something like that
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