If you feel Centrelink and the Government aren't listening to you or taking the #notmydebt issue seriously, contact your Member of Parliament.
It's your Member of Parliament's job to represent all the people in their area (even the ones who didn't vote for them), and many have been helping individual constituents work towards resolving their Centrelink debt issue. Ring their local office (not their Canberra office) and ask for an appointment.
Entering your postcode here will get you the name and contact information for your local MP (if you want to suss them out first, They Vote For You will show you where they stand on a range of issues).