1. Send them a legal notice demanding the total due amount with interest if they are not obliging to pay move to a civil court.
2. You should file civil suit suit to recover the amount due.
3. You have demanded the replacement of the raw materials and the delay was also explained to them so if they did not want the delivery they could have cancelled and also they waited two month to excuse to pay the amount and returned the goods.
3. Since you have the documents proving the transactions and delivery of the goods, have got a strong case.
Get the help of an advocate and first send the demand notice then proceed in the court