Is your therapist a member of the BACP? If so, you do have grounds for complaint. Here are the ethical principles BACP registered therapists must uphold:

Being trustworthy: honouring the trust placed in the practitioner.
Autonomy: respect for the client’s right to be self-governing.
Beneficence: a commitment to promoting the client’s wellbeing.
Non-maleficence: a commitment to avoiding harm to the client.
Justice: the fair and impartial treatment of all clients and the
provision of adequate services.
Self-respect: fostering the practitioner’s self-knowledge, integrity and
care for self.

It seems to me he has broken 'being trustworthy', 'autonomy' (by trying to convince you to keep working with him), 'benificence', 'non-malificence' and 'self-respect' (by not having adequate training in this area). It's pretty bad. And i don't think he knows it fully because he continues to breach his responsibility to value your autonomy in deciding whether to return.

If you are interested, here are some of the previous complaints which have been heard and sanctions imposed by the BACP Hearing Findings, Decision & Sanction - BACP Professional Conduct

I know this might not feel appropriate for you right now and that's understandable, but it could be something to bear in mind if you ever wanted to go down that road. I'm sorry your therapist proved himself to be completely incompetent at working with sexual assault.