Bank customer’s last payment is returned (4)
I believe the answer is:
reef
'bank' is the definition.
(thesaurus)
'customer's last payment is returned' is the wordplay.
'last' indicates one should take the final letters.
'payment' becomes 'fee' (I've seen this before).
'is returned' shows that the letters should be reversed in order.
The final letter of 'customer' is 'r'.
'fee' written backwards gives 'eef'.
'r'+'eef'='REEF'
(Other definitions for reef that I've seen before include "Chain of rocks near the surface of the sea" , "Ridge near the surface of water" , "Rock near water's surface" , "endangered habitat" , "Coral or rock just below sea surface" .)