As already stated , Openreach ( not BT ) installed your FTTP and made it available to all ISP’s that want to offer service over it , you chose BT ( even initially you had a choice of providers , that choice is greater now than a few years ago , because some ISPs that originally ignored OR FTTP now chose to consume these OR products )
Because BT used the common OR records to get you connected, it proves the ‘records’ were fine , otherwise BT wouldn’t have been able to get you connected ….
You say you have checked comparison sites and can see cheap FTTP offers , but when going to the individual ISP’s websites , you are only offered slow speeds ….there are many ISP’s that don’t have comprehensive nationwide coverage , so in one area or region they may be able to connect someone to OR FTTP ( because they invested in cable links in that area ) but in another area or region they cannot , and they only offer ADSL/VDSL because they haven’t yet ( or don’t intend to ) invested in the required cable links in that area , (cable links essentially are a connection from OR equipment into the ISP own ‘network’ ) so the headline on the comparison site no doubt has a disclaimer about coverage …..or it could be you looked at ISP’s that can offer FTTP via Alt Nets , but they don’t use OR , so if your property only has FTTP from Openreach, then these ISP’s , although on comparison sites , are of no use to you.
You need to be more specific, post your result from the DSL checker ,
https://www.broadbandchecker.btwholesale.com/#/ADSL
Give an example of an ISP that offers FTTP over OR ( check on the OR website for ISP’s that consume OR FTTP ) but cannot service your address
