Get online support
My land line has stopped allowing me to make calls but there are no issues receiving them. This happened a week or two ago , previously phone was working fine. I have nbn and that is fine.
If your NBN service is ok (means the speed is correct and you dont have any issues on browsing).
I may advised you to factory default the TPG modem.
Pressing the pinhole on the back for 10 seconds.
The link below relates to problems connecting to internet. I have no problems connecting. The only issue is being unable to make calls.