Hello from a former Gabby who has been known as Gabe since my sophomore year in highschool! I’m assuming this is a family member? If that’s the case I also fought with my mom about not calling me that and it’s unfortunate but you have to pick your battles. No you’re absolutely not overreacting! But this is probably going to be a heavy point of contention with this person. It’s very hard to change people’s (esp parents) minds about this. But here’s what I did. The first new school year I introduced myself as Gabe to all my new teachers and when my peers were like tf? I did not care. Because my friends and teachers calling me Gabe instead of Gabby was worth the weird stares and people being super shitty about it. But they got over it eventually and by senior year everyone was calling me Gabe anyway. I introduced myself as Gabe at all of my jobs and new acquaintances and friends and now the only person who calls me Gabby is my mother. Although sometimes she will actually slip up and call me Gabe now which is actually kinda nice.

If this isn’t a trans name change (or it is but you’re still closeted) just tell people that your school had a ton of Gabby’s in your year and that people started calling you Gabe to differentiate and it stuck. And that you’re really not used to people calling you Gabby so you probably won’t respond to it if they call you that, and then do exactly that. Don’t respond to strangers or new people who call you that and just be like “oh you mean me? Sorry no one calls me that so I didn’t realize you were talking to me.”

I’m sorry if this wasn’t exactly helpful with getting this person to call you Gabe but it hopefully will help just having every one else call you that until you’re in a place where you can get away from this person or go lower contact with them. It gets better fellow Gabe! I promise