Air India — refund not yet done

I booked a ticket from Bombay to Delhi on 30th july'2018 for 3rd nov'2018 through air india's app in the name of 2 passangers- Aakriti jain and Taru jain. My transaction was completed but the ticket was not generated due to some technical glitch in the app.
I called the customer care, and they told the refund will be done.
so, i booked another ticket through my laptop on the very same day due to urgency.
later, due to some reasons I had to pre-pone that ticket to 30th october'2018 and paid additional amount as required.

I've been calling the customer care since then and just getting the reply that the refund will be done, but still no action has been taken. I've written several mails too regarding it but no revert has come.

I've talked to my bank (Canara Bank) and they have given me a official written statement that the money is not with them, it has been sent to Air India through online transaction.
I request you to take action against my refund not being processed since it has been 9 months now.
Being a student that amount of money(Rs 8090/-) is very much valuable to me.

Transaction date Ticket date From-To
Amount
30th july 2018 3rd nov 2018 (preponed later) BOM-DEL
Rs 8090 (deducted twice- to be refunded once)
21st oct 2018 30th oct 2018 (traveled) BOM-DEL
Rs 7192 (extra charges for pre-ponning)
1st aug 2018 11th nov 2018 (traveled) DEL-BOM
Rs 7830

Name of the travelers- Ms Aakriti Jain
Ms Taru Jain
Registered e-mail- [protected]@gmail.com
Registered mobile no.- [protected]