@Darrenmusson With the change was it sky to sky and possible router change over or not keeping the old router, but the engineer connected you up to the fttp service and left it that way for you to carry on using it as a fttp connected internet.?
What lights etc are on with your router and also on your new ONT that (OR Openreach) has installed, you may wish to power that off for a couple minutes also. No rapid off/on leave a few mins...
