If you're on an FTTP Priority exchange and they think FTTP is available to your then you can't buy FTTC.
As above, there's no such thing as an FTTC cabinet with no equipment inside.
You're connected to a PCP cabinet that contains no active/powered kit, only copper wires. They have no power supply.
When a cab is upgraded to FTTC they build a completely separate cabinet for the FTTC equipment, complete with power supply.
The engineer surely can't miss a whole cabinet.
Usually we would obtain the exchange and cabinet number and do a lookup on Google Street view to see if there's a physical FTTC cabinet. If you know the location of your cabinet you could take a walk round and check yourself. If you fancy that someone can explain how to find your cabinet.
There's also a couple members with access to data that isn't available to the public who can sometimes lookup info for you.
Database errors also exist. I've seen cabinets show FTTC where none is available, or the records may show you connected to the wrong cabinet.
As advised above you could order FTTC separate to your ADSL and then cancel the ADSL if/when the FTTC goes live.
You won't get moved to 18/2 FoC.
VDSL2 18/2 doesn't exist any more. It was only a trial speed tier and was withdrawn from sale although those already on it were allowed to remain.
I think they might have left 18/2 on the Chelsea exchange as the exchange was closed and moved in to another exchange, having a big impact on ADSL speeds.
It might be gone there as well though.
There are providers that will move you to 40/2 or 40/10 for the same price as ADSL though.