My step-granddad is a complete bastard. Advice please.?

My step-granddad and I have never got on. He used to physically hurt me ALOT and I rather not get into it but he tried to drown me in the swimming pool. At my brother in law's welcome home party my step-granddad went for me in front of my cousin and my other brother in law. He also hit me in the back in front of my girlfriend. Well tonight he came round to mine and my mums house (I'm 15) to pick up something, my mum told him that we didn't have it and we would of got it if he had given us warning. He started shouting at our door and I went to see what was going on and he said pointing at me, "Look at her, common muck. People like her are disgusting." My mum slammed the door in his face and we thought that was the end of it. But then we heard banging and crashing round the back of our house and we ran to have a look and my step-granddad was trying to get into our garden. So I shouted at him to get away and that we would call the police so he stopped and said he wanted what he wanted. So I went round the front and gave him something that looks like the thing he wanted and handed it to him. I told him he broke the gate and he told me to grow up and stuck his middle finger up at me and sped off in his car. I am so mad right now and so is my mum. It's like my nan is brainwashed by him. He has physically hurt me in the past and I just don't know what to do. Surely what happened today isn't the end of it and I don't know what to do. What should we do?? SERIOUS ANSWERS please.