@Vlad ********
had exactly the same two weeks ago.....so frustrating...took everything....proof of rental, letter from immigration, passport with the non o 90 day stamp.....Three banks still said no......two said only if married and two iinsisted it was only a tourist visa......luckily krungsri agreed...
It's become like chicken n egg.....immigration want bank account to do the extension...bank want extension before giving account....basically immigration and banks have no connection.
Simple solution...bank let you open an account. Deposit money but not make it usable until you go back with the year extension in the passport..