You said that Openreach only provide line routing data (which is incorrect in this case as their checker shows fibre is not available despite the correct cabinet number showing). This is not true, the provide the speed estimation data too.
You said that it's Wholesale data which is wrong which is not correct.
Wholesale get their line data from Openreach, so if Openreach data is wrong, then the data BT Wholesale hold is wrong.
The issue is with Openreach data.
I think you'll find you're mistaken.
Could you explain where Wholesale get there information from such as cabinet number?
Can you explain why on the Openreach checker, the OP's line is showing as connected to a cabinet which neighbours can get FTTC services however the Openreach checker and therefore, Openreach data, advises his line is possibly too long?
If the OP were to order through Sky, who do you think Sky would approach to have data rectified? It wouldn't be BT Wholesale, as they have no business relationship with them. It would be Openreach, as Openreach provide the line speed estimation data.
The speed estimation data is produced by Openreach depending on the line length, celerity line loss amongst other factors.
This data is provided to all BT Wholesale alongg with LLU providers suh as Sky and TalkTalk.
You don't know what I know or my background, so your statement is a bit bold.