You can only get the database corrected by applying for a phone service from a provider who uses Openreach, or if you already have a landline phone provider, they can request an update.
Excuse my ignorance but I’m looking at another provider and they are quoting me a fee for the installation of a line. I already have a bt line from being with sky that is inactive so is this charge jus to reactivate it rather than install it?
The charge is raised by Openreach, whichever provider you use. The old external routing would have been re-used for another customer, so a new routing would have to be built.
Your old line would be an Openreach line, not a BT line, as there is no such thing any more. Sky would have rented the wires from Openreach.