So sorry you are going through this. If it was me, I'd approach it as 2 issues.
First issue: you need to ensure that you are not going to be subject to disciplinary proceedings resulting in a warning or worse.
Has the complaint been set out in writing? Make sure it is given to you in black and white.
Make sure you have a clear account of exactly what the complaint is. Don't try to second guess it by trying to figure out what they think they thought you said. If the complaints are not clear/make no sense, require that they clarify them. Also require proper citations, i.e., "On X date, in Y document, RightSide said Z".
Answer each and every complaint in writing, citing evidence (or lack thereof in respect of the false claims). Take this to an employment solicitor and get advice. Make sure it is just right, and make sure it is filed with HR under cover of a formal letter , preferably from a solicitor.
Don't attend any meetings without a witness present, again, preferably a solicitor, but otherwise someone you trust. Take someone reliable who can take copious notes while you talk/listen (very hard to take notes and absorb what's going on when you are scared).
Though even if I had said what I understand they claimed I said, I don't think it would be worthy of complaint).
I wouldn't go down this route. Just cold hard facts: this is what I said, these things I did not say, none of it was transphobic (or whatever their complaint is).
So second issue: you say you want to make a stand. If/how you do that depends, I would have thought, on the outcome of the first issue, and will depend on your employment environment as to what is appropriate. It may be achieved simply by dealing with issue 1. Hard to tell without further details.
Good luck 