Brief summary of context. I socially transitioned before he was conceived. His birth mother left me before he was born. I spent 18 months fighting to even meet him. Eventually had things going smoothly with overnight time. Then the birth mother cut contact again. I've only just got to see him in a supervised context.
Near the end of the last session I referred to myself as mummy Eve, as I've done thousands of times in the past without issue. This time he yells that he hates it when I say that. He goes on to say I'm just pretending, I'm not a mummy I'm a he, and he knows I'm a he because I'm wearing a top.
I'm certain he's getting this from his birth mum. I'm devastated, it pushed me closer to giving up than I have been for a while. I don't know if there's anything I can do about it in the two hours a week I have with him. (At least for now)
I'm sorry you're getting some dismissive comments. I'm a trans parent of a 4-year-old, so I understand how hard this must be.
I'm fortunate enough to still be married to my daughter's other parent, but I can tell you that if both parents aren't be aligned on how your child should refer to you, it's going to be very difficult and confusing for them.
Because of this situation, above all, give your son some grace. He is going through something very challenging and confusing at a pivotal stage of his development. Divorce is really hard on a kid, even the ones that go "smoothly" (my parents got divorced what I was ~12, so I know first-hand). It does seem likely that he's getting mixed messages from his parents, so be patent with him and just focus on being the best mom you can to him.
It's okay to gently correct him, but don't press the issue too much, or you'll risk making it worse by placing additional emotional burden on it. Something like, "I identify as a woman, and it hurts my feelings when people call me 'he'," is plenty.
You simply aren't in the position to compete with the amount of time his other mom has to sway his opinion, so don't try. Just be consistent, be gentle, and make the best of the time you get with him. Hopefully one day he will come around once he becomes more capable of forming his own opinions.
At the end of the day, your guiding light should be to do what's best for your child. Don't try to convince people you are right. Focus on trying to do the right thing.