The phrase "προς Θεός" does not exist in modern or in ancient Greek. It is grammatically wrong, because "προς" is a preposition and it is never followed by Nominative Case (Θεός is Nominative Case).
You probably refer to the phrase "Προς Θεού" (Θεού is Genitive Case), which means "For God's sake".
It is used very often in modern Greek to show strong objection.
Προς Θεού, μην το κάνεις αυτό! = For God's sake, don't do this!