Cancelled most of them -- log unofficially (3,3,6)
I believe the answer is:
off the record
'unofficially' is the definition.
(I've seen this before)
'cancelled most of them log' is the wordplay.
'cancelled' becomes 'off' ('off' can be similar in meaning to 'cancelled').
'most of' means to remove the last letter.
'log' becomes 'record' (I've seen this before).
'them' with its last letter taken off is 'the'.
'off'+'the'+'record'='OFF-THE-RECORD'
(Other definitions for off the record that I've seen before include "Not to be made public" , "in private" , "What you take when the disc finishes" , "unprintable" , "not intended for release?" .)