Maybe it might be better and remain with BT, I know it’s not what you wanted. But looking at the issues it’s created that I think is your only route, unless someone else comes up with another idea, because the only problem I had when switching to Full Fibre wjth BT was that they wouldn’t drill a hole in a uPVC window frame.
But as my mother had died, I had a spare Sky setup, so Open Reach were able to feed the cable through the hole that Sky had drilled, which got around the problem.