There are several types of NBN connections. NBN can be connected directly to the premises or building, FTTP (where your lead-in cable is optic fibre) or to the curb, FTTC, (where you still rely on the existing copper lead-in), or fibre to the node, FTTN (where your lead-in and cable in the street up to the node is still copper). In all of these options, the internal cable is still copper. Then there are areas that are NBN via Satellite.
Optic fibre cable is glass and can easily be damaged. If your Fibre lead-in is damaged, you need to contact your provider and report the damage. If your lead-in is copper, you will need to contact OSA Communications.
Where you have fibre to the building, you will have in place, a single core fibre cable from the external NBN box to the internal modem. If this is damaged, call OSA Communications.