Hi Dani,
As to whether you have made a huge mistake, I wouldn't be so quick to start bashing yourself up. In general you have made some very appropriate decisions, carried out some respectable research, engaged in a practice of due diligence, and in many aspects, have moved forward in your journey. I wouldn't call that a huge mistake by any means.
In any matter of uncertainty that we engage in, be it legal, financial etc, we have to engage in some sort of basic trust relationship with our providors. Due to our lack of knowledge and experience in those respective professions, we can't be held responsible for the inappropriate behaviour of those we have engaged. However, we have a duty of care, to ourselves once determining such activity, to correct the matter immediately in order to minimise any further risk. To which you have done. I feel you have handled the situation, respectfully, sensitively, with a great deal of maturity.
Although some good has come from your association with the therapist, I think he may have taken advantage of some aspects of the treatment. Directing you to specific providors when there is the possibility he receives a commission. Somewhat unethical due to a conflict of interests, only if it is true.
The good news is, although you may not actually have a letter authorising your HRT, by virtue of the fact you have been on it for a considerable period of time, if you were to contact a local Endo you should be able to continue HRT, with the possibility of it being covered by your insurance.
As for your therapy, although somewhat misguided by very obscure prognosis (Viz: lose your male persona and gain your feminine voice) I sense you may have had some value. You are the one that can really answer that one.
At least you are now aware and sensitive of the fact, not all professionals have our wellbeing as their principle focus. Which has to be a good result when you consider the remaining research you have to do with the rest of your journey. Where ever that may take you.
I think you need to pat yourself on the back for what you have done. I wish you every success in correcting the matter, and in the meantime, be safe, well and happy.
Lotsa huggs
Catherine