Exprted goods return with payment of custom duty

Dear Experts, We are manufacturer of exported goods. We have sale exported goods under rebate claim of duty and submit final proof of export. After one year the Buyer rejected our goods due to quality problem. Now we have received this consignment for payment of all custom duty & fulfill all import obligation in custom. I want to know your advice that would we reverse all export benefit and treat as export return.However we have paid custom duty. Thanks