Have you recently renewed your contract, as that seems to remove it, and you have to add it again?
No, have not renewed recently. This has happened before and took BT several attempts to fix.
I cannot find any previous post on this forum from you, relating to this.
Please check to see if Caller Display is switched on by entering the code * # 234 #. If it's active you'll get the message Caller identity will be displayed.