Return it right away. Visa MasterCard system is universal. Your record belongs to the world, too. This will deal a fatal blow to your future loans. If someone else's repayment interest is 4%, you may become 6%. You can pay it back through online banking. If Australia is ANZ, it also has branches in three major cities in China. If you don't pay it back, there will be great obstacles to opening a credit card in the future. The overdraft limit will be low.