You could try this link
https://www.openreach.com/forms/fibre-broadband-availability---customer-form
Basically there is a section to fill in along the lines of ‘my neighbours can get FTTP but I can’t’ …that gets OR to check the address and build plans etc , and if it’s just an error (so for example a CBT were provided outside the building specifically for the flats and at each occasion when a flat ordered service , a tech had to pull a single service cable into the building from outside , through the common areas and into the individuals flat ) and the assumption is the person ordering has gained permission from the freeholder or whoever to cable in the common areas , then the availability is changed to show that with the appropriate notes about extra work etc ( in other OR just need to correct an error showing no availability to showing availablity ) , but in my opinion that is very unlikely to be the case , the most likely response would be as your address is part of a MDU it’s a separate build so your SDU neighbours having FTTP doesn’t actually help you at all.
