Air india - Unexpected cancellation of ticket

Sir
I'm sending this email to bring your attention to a very important issue.
I had booked a ticket in Air-India from Cochin to London on */*/**.My ticket got cancelled and hence I booked another ticket from Cochin to London via delhi on the same date through a private agency. We got a mail confirming the ticket from the agency.
The departure time was Indian time*:**pm.We reached the airport around *:**pm. While we were checking in we were told that our ticket got cancelled. The authorities were unable to give us a convincing reason for the cancellation. While contacting our agency we were informed that it's a fault from the side of Air-India. We waited there till *:**pm. I travelled nearly **kms to reach the airport with my two kids. I was travelling all alone with my * year old son and *months old daughter. In such a situation you can imagine the amount of mental stress and pain along with physical discomfort me and my kids have went through. My husband was waiting in London expecting our arrival. We had to undergo RTPCR test twice. We had to face a fair amount of financial loss.
I think I'm eligible for compensation from your part for undergoing terrible mental and physical stress along with financial loss.
I hope you will positively accept my demand. Attaching my flight tickets with this