Hello Mouli, Greetings!
Let me help you.
I would suggest you to reach out to CSAB officials as soon as possible regarding your fee refund. You can contact them using below details:

Central Seat Allocation Board – 2019
National Institute of Technology
Tiruchirappalli – 620 015
Tamil Nadu, India
Contact No. : +91 431 2504333, +91 431 2504334
E-mail : csabhelpdesk.nitt.edu
Timings : 09:00 AM to 08:00 PM (Monday to Saturday) , 10:00 AM to 06:00 PM (Sunday)
Thank you, best of luck.