You can only sell overseas once you have a feedback of ten or more I think. It sounds like you have registered in the UK so they probably have the same rule.
As your feedback is only 4 you do not have much to lose. I would close the account and open a new one and make sure you are signed in to Australia when you do it.
Otherwise you could try asking somebody fromEbay what is going on but be prepared to spend a lot of time or possibly several calls as customer support is definetly not renowned for giving customer support.
