Not those in the services (5)
I believe the answer is:
these
'not those' is the definition.
(I've seen this in another clue)
'in the services' is the wordplay.
'in' is an insertion indicator.
'services' becomes 'es' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'the' enclosing 'es' is 'THESE'.
Can you help me to learn more?
(Other definitions for these that I've seen before include "See 13" , "Pronoun for people or things" , "He set (anag)" , "Sheet (anag) -- pronoun" , "Plural form of this" .)