that is bullshit man auspost should take full responsibility. They ran over the package, the package didnt just get damaged whilst in transit.
Also i bet you can prove that it is impossible for those 1 touch cases to possibly break any other way. Just those cases alone should be considered highly safe way of posting cards. Keep us posted on what happens. I'd go as far as finding out what warehouse it went through and go from there. If you took this far enough they would have to have video footage in warehouse showing clear neglect or at least show they are at fault...