My understanding is that therapeutic privilege only applies if through the disclosure there would be an imminent serious threat. Like if a client had said previously "I couldn't take it if I were diagnosed with BPD, I'd just kill myself if that happened" and the therapist does indeed believe that this person has BPD, then the assumption could be made that this threat was meant seriously and also that due to the nature of BPD the risk even further increases, thus the diagnosis is not disclosed.

The refusal to go back to therapy if somebody is not happy with the diagnosis or similar things is not ground for therapeutic privilege.

To me, it would depend on how this is affecting your life. As Favorite Jeans said, are you doing a formal complaint to an external body? If so, I don't have much experience with this, but I'd assume you would put this point down as one of the complaints and hope they agree with you.
Otherwise, is the information saved anywhere, like if you go to the ER, will the diagnosis be there for them to see right away, something like that? This would affect your life significantly and in that case I'd probably try to find out how you can get that deleted, I'm sure there is a way, mistakes happen and if you have proof from other therapists saying it's wrong, that should help.

If it's neither of these two situations, I'd not contact that therapist again and try to move on, maybe with the help of another therapist.