What G&S said. My gelding was totally against any bit when we met. After trying a lot of different ones (all smooth), he now goes very nicely in a loose ring French link Neue Schule bit. My mare, who was even worse, is doing quite well now in a Neue Schule Verbinden (or maybe it is Verlinden, can never remember). You really, really want to use the very least bit possible, and use your muscles (all of them) to get your horse to respond as you wish. I’d almost recommend using a bitless bridle until he has recovered from the abusive bit he has been suffering.
As for the muscles, I do not mean heavy squeezing, kicking, holding tightly to the reins or anything like that. Small weight shifts and gentle leg pressure should be all you need, along with back, shoulder and core muscles. Try teaching him words to go along with it – Joe Joe will now do circles, reverse, figure 8, serpentine and spiral on word cues only, as well as WTC. He will even do the WTC from point A to point B when I tell him. We are working on his lateral movements. Selena is still learning words, but has come along nicely, with the exception of “stay” or “stand”. I find it creates a better connection if I talk to them a lot.
It is never the horse's fault