I completed my high school graduation in 2012 and school closed in 2014. I am looking forward to take admission in this university but university wants transcripts in closed envelope from school. What do I do?
The transcripts from you school must have gone SOMEWHERE.
It may take you some serious time-- start with your local education officials and find out where the records are being kept.
In the meantime, contact the university and speak to someone in admissions-- ask what they think you should do. and get their name, and address all further correspondence to that same person.
You may want to get a closed envelope from somebody attesting to the fact that the school closed.