I have been through the same situation with the Halifax. I have asked questions that I feel are vital to our case but never received any answers. Every letter I send them is replied to with the same content - "We have fully answered all your questions and will not correspond with you any further"(posted 7886 days ago)I have made a copy of all letters sent and received to the Halifax and contacted the Ombudsman regarding Halifax's refusla to answer questions relating to the case. The Ombudsman has now begun an investigation into the actions of the Halifax.
I suggest you contact the Ombudsman with a copy of ALL documents you have to strengthen your case.
Also it might be worth contacting the Data Commissioner. If you say that the bank have in the past given your girlfriend data relating to you and now they state that they do not have your authorisation then they could find themselves in breach of the DPA. They should not have provided your girlfriend with any data if they "claim" that they did not have your authorisation.
It is more likely that they have lost your authorisation (it has happened many times in my case). If you have proof in writing that they have sent your girlfriend details and also that they claim not to have your authorisation then the Data Commissioner can step in. Go to the Data Commissioners website and download a non-compliance form and send it off.
I have built up a very strong case against the Halifax and will not back down to their bullying tactics. I have involved as many external orgainstionas as I can in order to show the Halifax that they have acted negligently.
The Ombudsman should be able to help though.
Good luck with your battle!
Kaveh