Yatra.com — Full refund not provided for flight ticket that was cancelled by the airline

Website: yatra.com

I had booked a return flight ticket from Jaipur to Goa and back. My flight booking was partially cancelled (return leg from Goa to Jaipur was cancelled).
Jaipur to Goa: Rs. 11722
Goa to Jaipur: Rs. 11718
Discount : Rs.2000
Total ticket cost:- Rs. 21440/- (after applying my SBI discount coupon which I cannot redeem again)

The Goa to Jaipur sector flight ticket was cancelled so the ticket cost: INR 11718 (This is the total amount that should be refunded to me)

Yatra.com has deducted my SBI discount coupon of Rs. 2000 and this is going to be claimed by Yatra from my SBI card. I have earned this coupon on my SBI credit card over the last year. It cannot be redeemed again as the code provided is a one time use only, so in this case it should be applied towards my first flight booking which is confirmed. Jaipur to Goa: Rs.11722 - Rs.2000 = Rs.9722)

I have only received Refund Amount: INR 9718 (This is the wrong amount as my personal SBI coupon of Rs.2000 should be added and total refund amount should be Rs.11, 718)

It has been a month and numerous email correspondences through which Yatra is not agreeing to refund my amount of Rs.2000.
Their call centre number does not help since I am put on indefinite hold and the call gets disconnected after 10mins.

Kindly assist to get my full refund.

Thank you