Cancelling tickets - Vanuatu

I had three tickets to Vanuatu for family holiday. Cost $2500. Following travel advisory not to travel, I cancelled the tickets three days ago. Found out today Qantas only refunded $500- so I have lost $2000. Called Qantas and was told that I "should have phoned to cancel and I would have got a full refund". Now it is too late, and I only get the taxes refunded. Call centre woman kept saying that I should have known...but I didn't. I feel that this is so so very unfair. I have made case/complaint online but it just gave me a case number. Does anyone have any other advice? Thanks