No, you will need to take your prescription to a hospital GP and request the medication, as only they can dispense Oxy and only from Thai scripts, not an unknown overseas DR script.
i never said they would sign it, I just said your claim insurance companies do not confirm coverage and only tell you to claim is misleading, they do provide confirmation of coverage.
not correct, insurance companies confirm coverage all the time when you purchase. Its no difference. I get a letter outlining my coverage details, what is covered, how much is covered and any exclusions etc.
To clarify you can NOT go from Non-OA to Non-O inside Thailand. You must leave Thailand and return (on tourist visa as example) and then apply for Non-O inside Thailand or apply inside your own country for Non-O before you return.