You state you are being investigated for overpayments regarding Centrelink. If they are investigating, then there has been no charges made. Many persons are being investigated by Centrelink due to overpayments whether it's due to their mistake or your mistake. Best thing to do is to go to Centrelink and investigate into this situation and if you need to pay back an amount then they will be able to work out a payment plan.
Charges are usually made due to fraud. However, it is under investigation at the moment. Go to Centrelink, be helpful as possible and sort it out willingly. Many a time, it is due to misunderstanding or computer data error. Best to be forthcoming and work with Centrelink rather than worrying. Go and sort it out. Rarely are people charged due to overpayments as this is a common occurrence.
Best of luck.