Export - calculation error in invoice

Dear All,

Am in need of a BIG BIG advise from you on the way forward.

We sent a Shipment to One of SAARC Contry. By mistake, there was a calculation error in Invoice. The rates were charged just double.

Buyer has recd the cargo. Made actual payment to to the bank through TT, We have recd DBK against Wrong Value.

Now how to close? My Bank is not giving me remittance Certificate plus we have recd Excess DBK.

In Monthly returns to ST and Excise, this sale is booked correctly in Indian Books.

Kindly help !!

Regards,

Anil Aggarwal