when printing a "missing" you can choose the character that is printed i.e. 0
is the other way (without data step programming) also possible: when een var=0 treat it as a missing??
Again - where is the SAS code/program that references the FORMAT you created? You have not shared that information - and it would be best served by pasting the SAS log into your post-reply to show a DATA step with a PUT statement to demonstrate that the format is not being accessed.