Air India — Refund of ticket id no EMT70860695

I had booked three tickets from new delhi to san francisco (Usa) and return in air india flight through easy my trip but due to covid 19, the flight got canceled by airline company. The purpose of this trip was to attend my son's convocation in the santa barbara university of california. I approached the airline company to refund my ticket amount as i have no use to visit in the future because the convocation is not going to organize anymore. The airline company has allowed me to use this amount as credit and forcing me to use this amount for the next visit but i want my amount refund.