Get online support
TPG provide their own devices (TPlink/Huwaei), as part of the services included on you itnernet plan (such us VOIP)
However if you want your own device, you need to find first if that device is able to work with NBN.
There some lists about NBN compliances devices. Depends of your budget and needs.
Compliant nbn™ FTTN/FTTB VDSL2 Modem/Routers
TPG will not provide support on third party devices.