It costs £680 to go bankrupt, so it would be cheaper to pay the debt, they have no way of enforcing civil debt from the U.K in Australia, and even if there was, they wouldn't bother, its 500 quid , you will need to protect your parents from being bothered though, you could write, not call, with your Australian address, see what they say, first thing is. make them prove that you do actually owe them something.