So, quick update on this should anyone be keen to know. I had to (re)order my fibre 3 times as the 1st two times the address kept saying no Fibre infrastructure. Our complex had Fibre live, but the map was not updated. Long story short, they installed and I used the login details on the LTE router and at first it did not work. I then removed the sim card (kept it out and just stuck it to the back of the router with tape - not to loose it) and then rebooted the LTE router and it came back on, on the PPPoE setting, and its working perfectly!
So, if you have an existing B315 LTE router from Telkom and you are upgrading to Fibre on OpenServe keep the router, it will keep working if you plug the ethernet cable coming from the Fibre box into the WAN port at the back of the B315 LTE router (provided you've taken the sim out) and you use PPPoE with your Fibre ISP details.