Hi Trixie
From the brief details you have given, you have absolutely no grounds for complaint to the FSO. It's absolutely at UB's discretion whether they let someone take their name off a mortgage or not. The FSO would not intervene.
They are perfectly entitle to refuse you on the grounds that you have a tracker, or on any other grounds.
For cases like this, you have to persuade, not threaten.
Brendan