Getting out of control for hours

My son is almost 8, and homeschooled. He also has ADHD and is currently on meds, but I'm hoping that we can stop the meds once we get these skills ingrained in his mind. We started implementing this 2-3 weeks ago so I know it will take time. I stay at home with him everyday and although we used to have a great relationship, we don't have one anymore and I'm desperately trying to fix that. He used to be fine with homeschooling and our schedule, but now he's against it and always tries to get out of doing it or waits HOURS to start, then he gets triggered and upset. I try doing the calm down spots and rule of three but he doesn't care and goes out of control (hitting, climbing on things to get what he wants, ripping things off the wall etc.) I mastered my calm and try modeling that, but I just can't get him calm until he's ready and although he's gotten the 24 hours of no privileges, multiple times, he still chooses to try and get those things he lost (like snacks.) He also talks back and calls me and whatever he's mad at names (like idiot or stupid, which I've never called him things like that EVER) and it's a constant power struggle and he says he does this because he "can't control himself."
I just can't seem to get him out of back brain, even though I've explained that and he acts like he understands, he still chooses to do negative things. I'm seriously trying here, but I am exhausted and want to fix our family more than anything. Thank you for all you do and sorry for such a long message!