What should I do when CVASC did not received our applications ?

I posted our applications by Express Post about 4 weeks ago and when I rang up customer service about it and was told that our applications were not in their system. She asked me to check with Australia Post where they verified that the Express Post was delivered to the CVASC Post Box. I then rang CVASC back and told them that Australia Post verified that the Express Post was indeed delivered. The Customer Service insisted that our application was not in the system and did not offer to help to investigate whether our application was misplaced within their office or not been delivered by Australia Post. Passports are very important documents and if lost it is tedious to apply for a new passport and a penalty applied for lost passports. We have booked to go on a cruise in 4 weeks time and time is the essence. What should we do?