How can I stand my ground?

How can I stand my ground? I’ve been stuttering since I was a child and my sister has always been a bully, now that we’re in our teens she’s been very inconsiderate of my stutter, she is very bratty and entitled. She tells me to shut up when I try to talk and my parents don’t do nothing about it. I talk back to her but she seems to just add fuel to the fire by being more rude, nobody takes me seriously when I defend myself and it’s very hard for me to when all I get is ignored by my parents and bullied by my sister.