DeletedUser84
Governments, especially anti-freedom ones like Australia, really don't like monetary anonymity.
A credit card not tied to an identity is the very definition of that.
If you want a CC that can't feasibly be tied to your identity and are unwilling to violate the law then you are looking at a complicated chaining of legal entities across multiple selected jurisdictions.
It is expensive and doing it right will cost you tens of thousands of USD in initial setup fees and thousands more each year in maintenance fees.
Or you find some homeless guy with a government issue ID who is willing to be your front man for a hundred bucks and hope he doesn't tell the government about the arrangement.
Because if the government knows the ID or CC that was used then they can search for all SIMs linked to that ID/CC and mark any that can't be explained for detailed investigation. Note that doing this is likely a crime, consult an Australian legal professional for a detailed analysis.
You may also be able to get a physical prepaid SIM card at the airport. Or convince a tourist to let you use their identity for one. Some dude flying back to Brazil and unlikely to ever come back to Australia may well be willing to use their passport to buy you a reloadable prepaid SIM. Just wait a few months to start using it.