Air India — not refund the cash because the fight has been cancelled

Address:

Vishwashanti Pagoda road., 844128

Dear Sirs, Madams,

I booked an Air India flight ticket AI 234 GAGA-CCU on 28-Sep-2019. but due to something error, the flight had been cancelled. Therefore, i booked another flight for going to CCU, because i had to go back my country on that night. now, i come back India again, but the money still not return in my account. i am waiting for refund money from Air India until now. please, let me know how to get the refund for that incident. Thanks for your kindly and wish you service in the best way.
your customer,

LE QUY MAN