Dear ginganinja45685 ,
I did find a solution after I tried all possible options, Telstra shop couldn't help on three occasions big Pond telephone assistance couldn't help Telstra telephone assistance couldn't help NBN couldn't help.
Finally NBN operator suggested that I call the phone manufacturer of the Z TE phone, telephone Australia 1300789475
My phone is a "ZTE 83 Dave"phone.
His suggestion was to back up everything on my SD card to my computer remove the SD card and the Sim card and go to
contacts, choose options, click settings, click backup reset, chooseoptions, select factory data reset,choose options, click reset phone and it seems you're done the trick.
These instruction are a little bit scratchy so I suggest you actually contact the factory and get them to run you through it but most important before you contact them
back up all the stuff on your phone to your SD card
then back up all the stuff on your SD card to your computer good luck hope it works for you mine seems to been successful and solve most of the problems so far all seems to be working good.
Regards,
Billco1947