Your services will probably be disconnected and the legal process of recovering money will most likely start. Even if you are not in a position to make a contribution to your bill I would still contact accounts and let them know of your situation. It might also pay to have a read of the link below.
Speak with billing and accounts my friend. You can do that via the live chat link below if you wish. You may need to wait a while as it appears the Optus website has gone down.
Hey @Patipan! It's definitely best to discuss the outstanding amount with our billing team. If you haven't yet done this please send through a PM with your full name, account info and DOB so we can take a look.