Is that US$36 in the US store, or Aus$36 in the Australian Store? See Change your Apple ID country or region - Apple Support. It shouldn't be possible to change regions while you have store credit or active subscriptions but it seems that occasionally following a link to an item in the wrong store can achieve this. Try signing out of the store, then follow a link to an item in the correct store to see if that will take you in. E.g. The Doors on iTunes (Aus).
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