Lucky fish. Tried signing out and reconfiguring Apple ID on Mac with Messages and still no goFollowup.
All of a sardine the issue resolved itself.
The only thing that I've done since last posting, was logging into my profile on my daughter's Macbook (to do some maintenance updates) and I noticed that it popped up a message saying that my Apple ID was now active on (insert Telkom number here) - when I checked my phone I saw that the 'tick' appeared next to the Telkom eSim number under Facetime indicating that it's now active.
So it seems that fiddling about with all those settings above got it working somehow.