The police should have paid this long ago (3,4)
I believe the answer is:
old bill
'the police' is the definition.
(I've seen this before)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for old bill that I've seen before include "Police (sl.)" , "evidence of previous appearances in theatre" , "pound note?" , "British Bobby" , "Cops" .)