Hugs!
It sounds like you have a rebellion issue, not an obedience issue. Counting is not something you should do because it teaches the child to obey AFTER counting or because there is a threat involved. If I were in your shoes, I would not give him any other options but to obey or be put in time-out. If you tell him to do something and he refuses, promptly pick him up and put him in a safe, boring place. No books, no TV, no toys, nothing. He is only able to leave time-out when HE decides to do what he was told with a “yes ma’am!” to boot. If you have to do this 50 times a day for a week, it WILL eventually sink in that you are serious about his obedience and will not tolerate disrespect or rebellion.
Stay calm, don’t yell or get flustered with him. Just give a command, and if it isn’t promptly obeyed, calmly and gently remove him to the designated time-out spot, telling him that he may get up when he has chosen to obey. And, this is not to sound harsh, but don’t try using ADHD symptoms as an excuse of sorts for his behavior. Our dd exhibited ADD/ADHD behaviors for a long time before we discovered that she had sensory processing disorder. It is frustrating for parents and child, but even a child with these behaviors can be taught to be obedient and respectful.
I am of the opinion that if you calmly make his life miserable as possible and show him that he’s bringing it upon himself, he will have no other choice but to change his behavior. It takes consistency and patience to break this habit, but it is possible and you can do it!
I will be praying for you. I know how hard this is and what a failure you feel like, but you are NOT!
Blessings,
Lindsey
ETA: Also, check his diet for food sensitivities. Our dd was a different person when we removed artificial food colorings and flavors from her diet, as well as processed sugar, MSG, and other additives. And, children with sensory issues or ADD/ADHD thrive on good sleep, good food, and a consistent routine. I have seen what a difference these make in the overall attitude and happiness of my children, and we place a priority on those three things above everything else for their well-being.