Such incidents are not restricted to vietnam. They happen in Australia, in singapore, in thailand and other places.

I'm not sure if we are allowed to discuss this topic but its essentially discrimination.

You can talk to the hotel manager but if it was me, i would insist on some form of compensation whether in terms of points or credits towards the room. Unless the hotel takes a financial penalty, the staff will never learn that such behaviour or communication techniques are unacceptable.