I had those same symptoms once before on ADSL and it was due to a failed microfilter. While that is still possible on fibre, I'd be more inclined to say it's a line fault.
Simplest test would be to disconnect the fibre modem and unplug/remove the filter plate on the NTE5 leaving just the test socket exposed. Then try ringing your number and see if it works. Then try dialing out from the test socket.
If those both work, it suggests the filter plate may be faulty. If not, a line fault of some kind.