NEED SERIOUS HELP!!!!!!?

ok it alllll started last wednesday.i was at piano practice as i am every wednesday.but my sister left after she played because she had to go to dance cl.so it was just me and the piano teacher.i messed up on my notes so she just when crazy and cursing me out calling me lazy ***.and she says she now i dont like here and dat she dnt care cuz she don' teed the money.she called my 17 year old sis retarded,and i started crying .i think she mainly said all of those things because i was the only one there.she even called ME mean-spirited and she talk about my mom,and my dad is that we also.i dent like either of them but my dad is a different story.she came out to my dads truck and even told him.and y dad saw me crying and said i dent have to take piano anymore.but this is the part i really dnt get.just a few minutes ago he said i have to practice longer to get better at it!WHAT!?!i want to quit piano!i really want to lear n to play guitar.piano was nvr my idea,he MADE me play since i was 6.(im 12 now).what should i do or say?They r very not understanding and i dnt wanna talk to her.i tried to quit once because of the same reason but then she promised nt to yell again,well,that plan obviously did not follow through.dammit!like i said i dnt wanna take piano!i dnt wanna talk to her pr see her ever again and i need to know what to say to my dad.UGH!