Are BT your provider , or do you pay someone else for line rental ?
In the past , bringing the cable through a window frame was acceptable, but isn’t anymore, but obviously if you were not changing the window there wouldn’t any need for Openreach to move the wiring, so because it’s your actions that need the cable moving it almost certainly will be chargeable .
OR cannot bill you directly for moving the wire , and you cannot contact them , so you need to arrange this work with whoever you pay for your service.
