As already stated , nothing stopping you ordering with whoever you want to use and that ISP getting Openreach to correct any data inconsistencies ( ORDI ) then allowing you to upgrade to FTTC once that is done , what you ( quite unreasonably ) expect is BT to sort out the error so you can order with a competitor company….BT have exactly the same interaction with Openreach as every other ISP , including the company you would prefer to use.
If the previous occupant of the address had FTTC , then obviously it’s possible , even with the supposedly incorrect address info to get FTTC ordered , so if BT managed to do it , no reason why your preferred ISP couldn’t also arrange it.
Openreach don’t normally interact with consumers , so it’s ‘lucky’ that you got to speak to them directly, but they also shouldn’t have mentioned ‘BT’ , unless you indicated that it was BT you intended to use, it’s unfortunate that you appear to have been given the false impression that data errors like this are something that BT are responsible for …they are not, unless you were already a BT customer and the data error was affecting your ability to switch to someone else , but you are not a BT customer , so you are owed nothing from BT.
Very unfair to accuse me of being unreasonable - I know almost nothing about this stuff, and I can only go by what I've been told, which was to contact BT, as they were the former supplier. If that's wrong then fine, but there's nothing remotely unreasonable about working off the basis of information given.
It still feels like I'm not in a great situation. Whoever I sign up with, I'm basically agreeing to pay x amount per month for 18 months for 1Mbps broadband, and taking it on faith that they'll be able and willing to upgrade it. There's presumably no guarantee that I won't end up paying literally hundreds of pounds for a connection that's slower than my phone hotspot.
It's also hard not to feel aggrieved that the information is wrong in the first place - it simply shouldn't be.
OK, well it sounds like I've exhausted this particular avenue. Many thanks to those who tried to help.