I struggled myself trying to potty train my son, who "figured it out" within 3 months after I just backed down. He's yet to have an accident. The best piece of advice I got for potty training is start the summer closest to their 3rd birthday. You have plenty of time!
I agree with Lisa. It's turning into a power struggle for him. Remove all potty training related items from sight and don't mention it. I'm guessing he's already in underwear, so move him to pull-ups or diapers. I know it's taking a step backwards, but it actually works. Explain why he's having to wear pullups or whatever, but without shaming him.
When you have to change him, do everything in the bathroom, standing up, and don't make a big deal about it: just treat it as par for the course. Do a running commentary: Now, we are taking this off, and see, poop goes in the toilet...etc,etc.
Sorry for the extensive post ;)