ISA is a bank account no? I had a uk one years ago and same as a bank account. Im only going on what they asked from me but a bank account in your name with permanent adrees withe the required 500k thb or equivalent is what I surjest
it may be because to open my bkk bank statement you need a password maybe that's why they asked I did not question it just gave them what they asked. It took 7 working days for mine and that was including them asking for additional documents