This week please email the Vietnamese Ambassador to the United Nations with the same simple message. On the left click the button which says "Petition Official" then where it says "Permanent Representative of the Socialist Republic of Vietnam to the United Nations," also on the left.
In your email you may want to quote Articles 18 and 19 of the United Nations Universal Declaration of Human Rights:
Article 18: Everyone has the right to freedom of thought, conscience and religion; this right includes freedom to change his religion or belief, and freedom, either alone or in community with others and in public or private, to manifest his religion or belief in teaching, practice, worship and observance.
Article 19: Everyone has the right to freedom of opinion and expression; this right includes freedom to hold opinions without interference and to seek, receive and impart information and ideas through any media and regardless of frontiers.