@cwebber Do they do this even when they know your (new) name (Christine)? Or does it only happen when they have no indication of your intended gender?
@cwebber Well thing is while he is considered general neutral when discussing someone in the third person I dont think it would apply in a direct conversation. Like if im on the phone with someone and their voice is ambiguous I wouldnt default to he/sir. I'd probably avoid it using "you". That said im not sure there is a gender neutral sir.
Its a tricky problem I guess and like you say hard to address in the current language without making up new words, and we all know how well that goes over with gender language.
Its a shame to say you need to work on your voice and to put the burden with you, though likely that is the reality. I can only imagine how much it must also hurt CIS gendered women who have masculine voices.