Sorry to say, we wont got your querry.
Normally the Drawback is process immediately after filing of the EGM electronically and credited to respective account if dont have any query.
Since you are saying that the Customs have asked to produce the BRC, then it may possible that your Drawback is pending for credit.
If so, then approach to Drawback Department, take the Prinout of the Query. Forward the query along with the proper documents as asked in query on a letter head of your organisation and keep the acknowledge copy with you.
If the Customs have asked to produce the BRCs related to the Past Drawback Claims, then forward your reply in continuation with the letter received from Customs to the concern drawback officer along with the Copies of BRC's.
There is no specific format for this.