paper lost by sale tax dept.

Location/place: JAIPUR

Name of company/service: national saving certificate

we have a NSC that we have given to sale tax dept as a gurranty of a firm. when we were about to surrender our firm we tell sale tax dept. to give our NSC back.
Sale tax dept. tell us that they lost our papers and we people have to go post office to re issue that papers and they have given a written document in which they written to post office dept to re-issue the duplicate copy of that papers.
Post office dept is telling us that
they are not authorised to re-issue the duplicate copy of NSC only on behalf of that sale tax dept letter.
from last five years we are moving in both the dept.
Kindly suggest us what we need to do now. To get our money back.