Cst sales return transaction

Pls guide me correct procedure for CST SALES RETURN GOODS, GOODS ARE EXCISABLE GOODS

in case of cst sales return the purchase had raise cst bill agst c form(when they was return the goods to the seller) and they demanded c form as well as we also want c form from them for sales of goods .......

now query is cst was paid twice to the govt one from seller and purchaser when they sent rejected material to us (seller). IS ABOVE TRANSACTION IS CORRECT OR SUGGEST WT IS THE CORRECT PROCEDURE FOR CST SALES RETURN GOODS.....PLS NOTE THAT GOODS ARE EXCISABLE