Spice Jet Airlines — Ticket cancelled by airline but refund not given

Dear sir,
I have booked flight through spicejet but cancelled by airline now i am requesting them for refund but they said your money will be credited in our Credit shell which can be used before 31/03/2021 .but i am sure that i am not traveling for the next one year.in that case how can I use that credit shell.so I want full refund in my account.please look into the matter.