Bass Knife Lock

My son Tim has been addicted to Crack for the last 4-5months and he's going totally out of control, last week he locked me in the cupboard while his friends came round which i presumed were taking various numbers of drugs while listening to that awful drum and bass music he told me to be quite unless he would knife me i'm scared to go to the police or tell anyone in person i need some help people don't know what to do he doesn't let me leave the house i spend most of the time chained up in my room he feeds me thin slices of food under the door and a few pills each day and tells me to chill out bitch please help me im serious