Your history with Revolut or bank will be with them so sign in on another device and you'll see the history. Check you are backing up to Google / other automatically
That's the point of security, what they really need is a mix of Thai and English speaking security, try to talk the thick neck bloke down, if it doesn't work, the Thais step in and beat the crap out of him, seems fair to me
Pharmacies often sell them, in bar areas such as Ban Chang they will know where to buy. In Pattaya they are available everywhere, in Buakhao hawkers will constantly walk by trying to sell them