I've been there with the NHS. It has taken 7 years of fighting to get proper treatment, funded by the NHS but supplied by an external provider. I've put in formal complaints, involved my MP and used an advocate extensively. I've been through the attempts to diagnose me with a personality disorder instead, the repeated loss of my notes, people not returning calls even when I'm in crisis... the horror stories trail on and on. I did have one year of really good therapy with the NHS, but the rest was just a mess.
To be honest, unless you are feeling incredibly strong, I'd advise you to stop trying with the NHS and try to find some private provision. Some really good private therapists will reduce their fees if they can see you really want to work on it. If you want to persist with trying to deal with the NHS, I recommend finding a good disability advocate to support you