Mr.Subhajit,
The amount furnished by you is security deposit for proper payment of tax under WBVAT Act. It is a deposit refundable on closure of your business after veryfing tax liablity if any. If the deposit is in the form of NSC, FD etc, it will be refunded on maturity after collecting fresh security. Thanks.
Refundable after 1 year or 2 year of registration as the case may be, as per the Trade Circular No. 07/2015 dated 13-05-2015 issued by Commercial Tax Commissioner of West Bengal. You have to apply at your concerned Charge Office, and after necessary adjustment, the concerned officer will issue refund adjustment order (RAO) if applicable.