The price match is for Halo , so an existing Halo customer renewing won’t pay more than what a new Halo customer would pay , it’s not a price match against non Halo products , unfortunately many decide the £20+ (or more) premium isn’t worth the benefits Halo provides, but even so you can’t compare (for example) basic 500Mb broadband price to 500Mb Halo+ price , the guarantee although not particularly clear never offered to match a premium product to the basic product.
You appear to be having what seems a relatively common issue , in that once someone has Halo , getting rid of it is no easy task (short if leaving BT for another provider) but apparently it can be done , you just need perseverance.
As far as address issues , if you want to join Sky and their records show your address as not having a working service to takeover , that shouldn’t stop them creating an order for a new line rather than a takeover, plus if FTTP is available (as you suggest it is ) then the copper service is irrelevant anyway unless you want to keep your phone number (if you have one )
Is there unusual about your address , like has a prefix or suffix ( 1a Madeup Avenue, that type of thing ) or is a flat in a converted house, with multiple aliases, Flat 1, Top Floor Flat , Flat , 1Made up avenue, all used for a single address , you need to check the Royal Mail site to see if your address is there exactly as you know it , not similar, but and exact match , then get Sky to use that and order you a new line not a takeover , unless the keeping the existing landline phone number is vital , it should also be possible for Sky to use the UPRN if it’s a single dwelling, not a flat .
