So I had a little google search, and I found this charity which operates in the US and provides a 24/7 helpline, which is free AND confidential.
https://www.childhelp.org/hotline/They can provide you with information to help you find other charities and societies who can give you direct help in your situation.
They can also just talk to you if you need to vent or want a friendly person to talk to.
Most importantly they can get you help with child abuse, which you are suffering from. You may not have been hit but you've been threatened multiple times and you're clearly distraught.
Please, please, please give them a ring when you can.
Tell them everything you've told us, and they'll help you way more than any of us can.
If you don't feel comfortable phoning from your house, or don't want your mother to overhear you, then try asking a friend if you can phone from their house, or even using a local payphone if you feel safe there.
But do try and phone them, just to talk, and see what they can do for you.
1-800-422-4453