Man that is awful, OP.
I mean it's actually kind of scary how I can relate.
I had a terrible STEP father who was sexually abusive. Like your father, he would "make up" excuses to "punish" me in the same way you said, except for me it was sexual.
He also abused my two older half sisters (different father same mother). It really took a toll on my oldest sister who turned around and started abusing me. Saying "You're my HALF brother, I don't HAVE to love you the same way". Was just telling this, through pm, to another Gaffer the other day, how coincidental.
But anyway, she was so disgusted with me she would lock me in my room with no food or anything when my parents were away and she was in charge. It wasn't until I was around Middle school or so, when I spoke up and she allowed me to come out and get food or use the bathroom. "Well I wouldn't want you to STARVE, I guess" but I was still mostly confined to my room. Still, that was just a few hours. Hard to imagine if it were months at a time.
It was actually my oldest sister's boyfriend when she was in High School, that dragged it out in to the open and my mom (who was completely unaware) kicked him out.
I was just finishing Middle School then and I was an emotional, broken mess going through High School. Never went to prom, never really dated. If I ever ask GAF for dating advice and people wonder why I would be awkward, well THIS would be why, not that I happen to have an MLP avatar.
I'm 32 now, and I'm in a much better place, but it can still be an emotional struggle. I have moments of anxiety and lack of confidence. So if you ever want to talk, OP, I think I could be of help.