OneGiantStep

I don't have kids that age, but it may because you're too harsh.

You said you're at wit's end so likely you've lost your temper with him quite a few times. When you do that, he's going to remember the yelling rather than the principle. You could let him know that the behavior is unacceptable but do it in a respectable manner, a manner that you would like to be talked to; otherwise, yelling is just going to create resentment.

If you have to, use something as leverage, such as allowance or TV privileges, but be fair and consistent. Once the punishment becomes unfair or yelling starts, the child will remember the punishment rather than the lesson.