Contact Staff - Create a ticket [Submit a Ticket] and then log in to your account from the browser and make sure you are in your original zone, I mean make sure no VPN is connected, and try logging in and log out many a few times ( From that provided link) And wait 48 hours, So they can verify the actual location of yours and change the region of your account. I mainly think the new servers of Vietnam and Account transfer caused this bug/issue to happen.
Again, Contact Staff and submit a ticket to resolve this issue