Upset, cancelled dispatch, ignoring son (6)
I believe the answer is:
offend
'upset' is the definition.
(thesaurus)
'cancelled dispatch ignoring son' is the wordplay.
'cancelled' becomes 'off' ('off' can be similar in meaning to 'cancelled').
'dispatch' becomes 'send' (I've seen this before).
'ignoring' is a deletion indicator.
'son' becomes 's'.
'send' with 's' taken out is 'end'.
'off'+'end'='OFFEND'
(Other definitions for offend that I've seen before include "Commit an illegal act" , "Distress" , "Cause displeasure to, insult" , "Do wrong or cause resentment" , "Affront - break the law" .)