Welcome and thanks for posting!
Sorry you felt my colleagues were uninterested during the live chat you had with them. I am sure that wasn't their intention. It does look like a potential glitch. What were you using to check your speed estimate? Were you using your phone number or your address details?
If you're getting near the full speed on Superfast Fibre 2 with your current provider there is no reason why you wouldn't get that speed with BT Consumer as the fibre cab and everything would be the same and we always give you the fastest speed that your line will support.
As you are not a BT customer you need to enter your address and then post results. This will show range of speed