it could simply be the bank teller is embarrassed by her level of English and doesn’t want to interact with you so just denies. Or she can’t be bothered dealing with a foreigner.
Wang Chomphu here, so it would be really useful if you could obtain a list of documents required to open a bank account that specifically states that you need to be on an extension of stay in order to open a bank account. At the moment I am leaning towards miscommunication, lost in translation reasons for refusal. If true it would be a game changer for obvious reasons as you cannot get an extension of stay without first obtaining an account.
the problem here is that the branch is closed to new accounts NOT the documentation required to open an account. Your claim that you cannot now open a bank account on a Non-O is false.
not another one, here this particular Bank branch has closed new accounts for Foreigners completely. As you can read the OP was able to open an account with a Non-O at another bank.