Returning of documents while purchase return in excise

HELLO ALL

I HAVE A QUERRY.

WE ARE FROM PACKAGING AND PRINTING INDUSTRY AND WE HAVE PURCHASE A MACHINE CHAIN PULLEY ON EXCISE BILL. LATER DUE TO VARIENCE IN SIZE THE SAME WAS RETURNED TO PARTY WITH PURCHASE RETURN BILL WITH EXCISE.

NOW PARTY IS ASKING TO RETURN ALL THE ORIGINAL BILLS AND DOCUMENTS PROVIDED WITH THE MATERIAL INCLUDING TRANSPORTER COPY AND PARTY COPY.

THEY ARE TRYING TO CONVEINCE US THAT WE CAN TAKE CREDIT ON XEROX AND PRAISING US TO RETURN ALL DOCUMENTS.

AS WE HAVE TAKEN CREDIT OF EXCISE AND PURCHASE RETURN HAS BEEN ENTERED IN BOOKS OF RECORDS AND THE PERSON IN ACCOUNTS ARE OPOSING THAT WE CAN NOT PROVIDE THE ORIGINAL BILLS AND DOCUMENTS.

PLEASE ASSIST WHAT ARE THE RULES FOR THE SAME.

PLEASE REVERT AT EARLIEST.