Offset due — fill in form (9)
I believe the answer is:
nullified
'offset' is the definition.
(offset can mean to cancel out or nullify)
'due fill in form' is the wordplay.
'form' indicates an anagram.
'due'+'fill'+'in'='duefillin'
'duefillin' is an anagram of 'NULLIFIED'.
(Other definitions for nullified that I've seen before include "Scrubbed" , "Cancelled out" , "revoked" , "Abrogated" , "Made invalid" .)