WRONG IMPORT MATERIAL RECEIVED AND PAYMENT NOT DONE.

Hi, One of my Client Imported some spares from outside India, for which payment is not done( Usually they have credit understanding of 30 days). But in the recent shipment they received wrong items and exporter asking them to keep the material free of cost (very low value) and agreed to  resend the correct items as per PO, as it is their mistake.  Can anyone advise us, how we can close this BE outstanding at RBI and Customs level. Thank you in advance.