Being taken advantage of isn't new (4)
I believe the answer is:
used
'being taken advantage of' is the definition.
(use can mean to exploit or take advantage of)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for used that I've seen before include "Dues (anag.)" , "Sued (anag.)" , "Took advantage of" , "given employment" , "No longer new" .)