Sorry for not getting back to you, the good news is, it's finally working.
I was not in yesterday but Openreach came out and changed all of the cables, this didn't work, they didn't want to replace the ONT as they said it was tested fine and were about to leave again, but I left a checklist that included, ask them to phone DCOE following @Zarjas suggestion.
20 minutes later we were back online.
I'm so glad it's all back and running and thank you all for your comments.
BT managers gave us their backup 4G hub in case this happens again and some credit off our bill as this thread only covers half of the battle I've had to actually get this fixed.
Appreciate all your help!