FlySafair refusing to refund cancelled tickets

The Grahamstown Festival was cancelled and we tried to cancel our flight bookings. FlySafair refuses to refund us, and will only give a voucher, which is only valid for 6 months. But we are unlikely to travel anywhere this year and so are going to lose our money. FlySafair have also changed their policy since the outbreak of Covid-19. Previously the vouchers were valid for 12 months, now they've changed to 6 months. How can they possibly think this is fair practice in a time of crisis?