Air India Express — Air India Express Delayed Refund

Myself Aruna Rajendran, I booked a flight for my parents in April'21, below are the details
My PNR Number of airindia express :- PNR - QXVIJW
Travel date: 24th May 2021
cancellation date: 27th April.
Amount to be refunded :- INR Rs.40, 940.84(less cancellation charges)

This is regarding my parents earlier flight to Singapore from Chennai. I had booked our ticket for 20th April, But because of the developing covid situation as the visa to enter into Singapore was canceled and my parents were unable to travel on the said date. So I had called Air India Express customer care and cancelled my flight on 27th April 2021.
The customer care representative told me that a refund has been initiated and I would receive the full refund within 15 days, but it's more than 15 days and I haven't received my refund till Jun'21. So I called the customer care again and they told to mail me to [protected]@airindiaexpress.in, I got a email that they will revert back shortly.
Then I emailed again 9th July and i got reply asking me to be patience and support. But i didn't get the money back.
I had emailed again on 11th Aug got another response saying the refund amount has been processed to the card holders account shortly.
Still haven't received the money till today 21st September.
Please help me in getting my money back!