If this feature was taken down then perhaps BT should invest more time briefing their employees. Collectively, more than 6 hours of time involving three BT employees and myself have been wasted chasing a red herring!
It is time for a Moderator to step up and clarify. If "My BT" management of Call Diversion is no longer an offered feature, then employees need briefing and documentation needs correcting to avoid repeat cases of potential miss-selling.
The mods are on the case to get the website updated.