ok we need to find out what happened to the new line first thast had working bb on it.
i would guess that the new line still "has a working bb service on it" this would be according to bt retails billing systems but when you requested the renumber they have not done this right for you and openreach have bodged the job in the exchange and a simple call should sort that problem out.
Next would be dealing witht the "first line cant carry bb issue" why not ? get the call recordingslistened in to this iwll allow you out of the secodn line contract if this proves to be false.
As for callsign you cannot ask for a specific number to be allocated to this service so this is a no go for you.
You can renumber the secodn line with the first line number bu this is now a very difficult task due tot the different systems BT Retail now use as they no longer have acces tot the openreach ones, it is doable but you need ot speak to the right people to get it done.
my name has been changed to save me from more company disciplinary procedures.
whatever i say is my thoughts and not those of the company i work for