Necessecity excise sealing / stuffing for nepal export

we despatched the materials to SEZ UNIT chennai with payment of excise duty as we have no LUT permssion. Accordingly we  applied for rebate claim to excise authority along with counter copy of ARE-1 , BUT EXCISE DEPT ASKING FOR bill of export, Is there any prohivision for BILL OF EXPORT in this case ? who will issue ? What is the formalities ? Matter was happened in the month Oct-12, Excise telling w/o Bill of Export Rebate will not be allowed. Pl, advice.