My sister keeps hitting me and undermining me, what should i do?

My relationship with my sister has always been weird but I'm reaching my limits but i don't know what to do. my sister has always said things to my family members to make it seem like i was dumb. My sister is not doing well academically but I am the exact opposite, so my family members would say "you should not be good just in academics, you should learn how people talk to one another and deal with situations" so my complaints always gets ridiculed saying "its just her usual outbursts" so these past years i have distancing myself from my family because things like these happened very frequently, so whenever i came back from school i would just pick up my phone. I know not a great way to deal with these things. But when i actually want to talk with my family about this, I get made fun of, which i made very clearly that i did not enjoy this but my mother would insist it was just a joke. So my complaints about my sister to my family is to no avail. It seems that making fun of me has just become a trend because whenever I even open up my mouth my brother makes fun of me (my brother is 8, my sister is 18 and I'm 14). it has just come to a point i hate going back to my house after school. Today i asked my sister why she was taking my earring but she got agitated and insisted that earring was hers. So she grabbed my brother's nerf gun and hit me till it broke. many situations such as this happened in my life. She once hit me with a metal bottle so hard that i got a concussion but i woke a minute later. she also pulled my hair so hard that it even hurt to slightly touch my head. There has been countless of things like this but all of these would happen when my mother is not present. So when i explain to my mother what happened my sister would twist her stories. but she would always get caught due to the bruises she left. But she always only get a slight scolding and that's it, my sister is writing an medical exam to get into a medical school so my mother is taking extra care of her. my father also loves ridiculing me, I'm seriously tired of this. I don't know what to do, i need advice.