Cancel note I fully disputed (7)
I believe the answer is:
nullify
'cancel' is the definition.
(nullifying is a kind of cancelling)
'note i fully disputed' is the wordplay.
'note' becomes 'n' (abbreviation**).
'disputed' is an anagram indicator.
'i'+'fully'='ifully'
'ifully' anagrammed gives 'ullify'.
'n'+'ullify'='NULLIFY'
(Other definitions for nullify that I've seen before include "Declare invalid" , "Invalidate" , "Make invalid" , "quash" , "Neutralise" .)