Join with unappreciative person penning note (9)
I believe the answer is:
integrate
'join' is the definition.
(I've seen this before)
'unappreciative person penning note' is the wordplay.
'unappreciative person' becomes 'ingrate' (I've seen this before).
'penning' indicates putting letters inside.
'note' becomes 'te' (musical note).
'ingrate' enclosing 'te' is 'INTEGRATE'.
'with' is the link.
(Other definitions for integrate that I've seen before include "Incorporate into the whole" , "Get together" , "Combine into a whole, unite" , "Incorporate into the main group" , "Organise a get-together" .)