Keyhole Saw

Few days ago, I heard my mum scream from her room, so I peek through my parent's bedroom keyhole, and I saw my dad brought a rope and tied my mum in the bed and sometimes he whip mum and scratch her. It happens almost every night. Once my mom even begged my dad for forgiveness but my dad keep pushing her and sit in her stomach till she screamed so loud. Dad also pee over mum's body, and pee into mum's bottom. I secretly told about this to my mum, but seems mummy is too afraid coz she denied it and say "mind ur own business" and she told me never tell anyone and she forbid me from peeking through the keyhole. I think mum is a little bit depressed and frightened and might has been threatened by dad. How can I report my dad? should I contact police straight away?