Angore,
The inscription "Cong-Hoa Mien-Nam Viet-Nam" means "Republic of South Vietnam". It is the name the Communists given in June 1969 to the area in South Vietnam under their control. usually these stamps are described in the catalogues as NLF or Vietcong as other members already written. Here is an example:

Other inscription on NLF (Vietcong) stamps is "Mat-Tran Dan-Toc Giai-Phong (MT DT GP) Mien-Nam Viet-Nam" means "The National Liberation Front for South Vietnam". This inscription was in use from October 1963 until June 1969.
