Air India Express — Flight refund for cancellation due to covid restriction

I had an Air India Express flight booked for December 01st and a connection flight with Singapore Airlines to Australia. But due to the changes in Covid regulations brought by Australian Government on November 28th, entry was restricted and so couldn’t make the travel. Air India isn’t ready to refund the ticket for a cancellation that happened due to covid restriction implemented by Australia. The connection flight airline, Singapore airlines have already refunded the ticket price. Please help get the refund on Air Indian Express flight ticket cancellation which happened not due to any personal reason but due to country level covid restriction.