BT do have a service which may help, you could try it for a month to see.
This can also block withheld calls, but it will not tell you the actual number, but it still blocks it.
On your phone, did you make sure that Call Guardian is turned on, and that you normally see all callers number appear on the phone display?
Unfortunately we don’t have call protect in this phone as far as I’ve been informed.
Its not a phone feature, its network based.