Firslty, Sir, as it has been stated in your query that the period is over, but yet they are not giving NOC.
Secondly, in that situation, I advice you to give them a representation asking reasons if any for the denial of the NOC.
Thirdly, if they still do not give reply then you may have to approach the High Court for the same in Writ of Mandamus under article 226 of our Constitution.