Refund of flight tickets

In February 2020 we booked and paid 2 return flight tickets from JHB to Auckland NZL. The flight was supposed to depart on 12 June 2020. Ref BZA-***. The flight never realized because of Covid-19. After numerous request budget air still refuses a full refund and insist on a cancellation fee. How can a flight that never happened be cancelled? Very disappointing that they actually try to "*****" our money!