I'm currently on Superfast 1 but my area has recently had full fibre installed and Openreach & BT Availability checkers are showing it as available at my address, however when I login it's not showing in upgrades and if I try and place an order for Full Fibre 150 i get "Sorry, the package you've selected isn't available"
I seem to be able to order it from Sky however, but still in contract with BT until July
Try calling 0800 587 4787, they can check if the records are correct and take steps to resolve.
Call them. I had the same issue trying to upgrade to FTTP. If I checked on the web site without logging in then it was showing as available to my address. If I tried to see if I could upgrade when logged into my account, it said the service wasn't available.
I then had an engineer over for a different reason and he pointed out the FTTP box on the pole opposite my house and even identified the fibre lines from it going to some of my neighbours. He advised to call BT and point this out. I did and ended up having a full upgrade to FTTP within the week.