Invoice is must have document and mandatory for car transfer. Check on Book/Reg. Car if there is a STAMP "Original File Retuned to Owner" that it's pretty sure file is not with excise otherwise if STAMP is not there then you can go and check with them.
If the file/invoice is lost then you have to process the duplicate invoice. Long and hectic process....
Take advise from expert if you will have to go for duplicate invoice from company.
Thanks