I am trying to get my Nest router to work with the Sky Fibre Direct ...
I have the Router and 3 extenders which worked perfectly with EE Fibre Direct but for some reason doesn't work with my new Sky subscription do I need to buy a newer version of the Router?
Have you tried to factory reset the Nest Wifi pucks then set up from scratch after you switched ISP?
You'll need to both factory reset each puck with the physical button, and delete the network from your Google Home home.
Then set up from scratch:
If using an Apple device for the setup process, make sure you have no VPN enabled/ connected; not any 3rd party product, nor the "Apple iCloud Private Relay" ( https://support.apple.com/en-us/HT212614 ). And make sure the Google Home app has permissions to "local network access" ( https://support.google.com/chromecast/answer/7172427?hl=en ).