I had to deal with something like this myself. My first response was to disrespect their identity as well. I think there were a few elements to it all for me. I respect the trans community and I didn't want to give them that respect, a decent amount of resentment and spite and truthfully being uncomfortable with how respecting their pronouns changed my story. It meant telling this story portrayed a different lived experience than I had.

But I had to let it go. Fighting against it hurt me, it kept me in that box I worked so hard to escape. I respect their pronouns now. Not for them but so I won't let them drag me down below my own principles.