3 1/2 yr old boy won’t train

We have had a very difficult time trying to potty train our son. We’ve tried putting him on the toilet every 30 mins, he won’t go he just waits until we look the other way and go in his diaper. We have tried rewards, he doesn’t care. He doesn’t want us to get excited or tell him good job when he does go on the potty. We have tried ditching the pull ups and using underwear, he peed and pooped all over my house for 3 days but still never used the toilet when we put him on it. The only time he poops on the toilet is when we catch him starting to go and run him to the bathroom, and still a couple hours later he will poop in his diaper if we don’t catch him in time. I feel like we are failing him, what do we do to get him trained?