If OCBC does not answer, try opening a DBS vickers
cash account. Basically a brokerage account which you can still open by mail as a non res without residence permit or employment pass. DBS Vickers account comes with a personal DBS
bank account to ease international settlements which is your vanilla bank account. The same should work with iOCBC which is an equivalent brokerage account product.
Maybe these lawyers were talking about adhere circumstances which apply to corporate accounts. There's no ban on opening financial accounts without a face2face meeting in HK nor SG.