Air India — Ticket Cancelled but no refund received

My son had an international ticket booked (Ticket Number:[protected] via AIR INDIA online and made a payment through his debit card. AIR INDIA canceled the flight and said that the refund of the amount was processed on Jan 16, 2021 to my transaction account. However, the amount has not been credited to the transaction account. The bank has clearly mentioned that that there was no refund received. Air India refuses to give me a Transaction ID and multiple mails to Air India has not helped me get the refund even after 3-months!!