Air India — Refund for flight cancelled due to covid-19

I booked 2 tickets bearing PNR HTKDJ from London to Kolkata via Flipkart, But I could not avail the same due to cancellation of flight service between the UK and India. I, however, rescheduled the flight but this time too (E-TICKET NUMBER:[protected], EXCHANGE TICKET:[protected]; E-TICKET NUMBER:[protected], EXCHANGE TICKET:[protected], it was not possible for me to make the journey as prior to commencement of the journey, I tested Covid positive. I spoke to Air India about this and they told me to get my refund from my agent, Flipkart. But according to Flipkart, they tried to get the refund from Air India but was unsuccessful as the airline rejected the same. And now Flipkart is asking me for some evidence stating I am entitled to a full refund as the transcript between me and the airlines wasn't enough. And now I am unable to get a hold of the airline because they are neither answering my call nor my email.