Unseen helper’s paper and coin no longer used (8,5)
I believe the answer is:
guardian angel
'unseen helper's' is the definition.
'paper and coin no longer used' is the wordplay.
'paper' becomes 'guardian' (I've seen this before).
'and' says to put letters next to each other.
'coin no longer used' becomes 'angel' (historical English coin).
'guardian'+'angel'='GUARDIAN ANGEL'
(Other definitions for guardian angel that I've seen before include "Benevolent spirit" , "Person concerned with the welfare of another" , "One watching out for another" , "Friendly spirit" , "Protecting spirit (in this paper?)" .)