Air india - Money not refunded after flight cancellation

I had booked a two-way journey for my mother-in-law from Kolkata to London in January this year from Air-India. However, the travel couldn't happen because of the COVID lock-down. I had to cancel both the onward and return journey. I had cancelled this booking on *st May after having a discussion with Air-India customer care. I was told that remaining amount after deducting the cancellation charge will be refunded to my account within ** - ** days. It's been almost * months the money is not yet refunded to my account. I have sent multiple emails to Air-India but without results. Please help in getting the money back. Thanks, Tapobrata Guha