Today sent a mail to the Registrar (moilbuyback@bigshareonline.com) asking them to look into this matter. Last time when I participated in NTPC buyback, amount was transferred to account on the last day of settlement of bids. So, I was expecting the same i.e. on 21 February.
Registrar replied that I should contact broker as the settlement had been done on 18th Feb itself. So, I have now raised the matter with broker i.e. Zerodha. Waiting for its response.