Duty drawback

Q : WE ARE EXPORTERS OF KNITTED GARMENTS. WE HAVE A FACILITY OF AVAILING DUTY DRAWBACK AS PER INDIAN CUSTOMS NORMS. FOR AN EXMPLE ,ONE OF OUR INVOICE VALUE IS EUR 40,000. SOME OF QUALITY PROBLEMS BUYER SUPPOSED TO PAY ONLY EUR 35,000. WE ARE ACCOUNTING BALANCE EUR 5000 UNDER REBATE &DISCOUNT ACCOUNT. WE ARE RECEIVED EBRC FOR EUR 35,000 ONLY. BUT WE HAD RECEIVED DRAWBACK AMOUNT FOR FULL EUR 40,000. IN THESE CASE WE ARE PAY ANY DIFFERENCE AMOUNT  TO CUSTOMS ? IF YES  HOW TO PAY? ANY INTEREST SHOULD BE PAYABLE? WHAT IS THE CALCULATION ?