Maybe just re-thinking about how you are asking him to turn and give to the bit will help. (Provided we get any tack issues solved.)
Starting from the ground ......
Let's bend to the left first. Stand at his side by the left stirrup. Take a hold of the left rein and gently but firmly add pressure and hold steady until he responds. Do not pull harder; keep the exact same tension on the reins even if he starts moving his body and trying to walk in a circle (which is okay in the beginning). Just keep your same body position and the same pressure on the rein even if you have to do it for 10 minutes. The very instant he creates the smallest amount of slack in the rein by giving to the pressure on his own, you need to release the rein immediately. You don't need to give him any extra praise, because releasing the pressure of the rein is his reward for correct behavor. Allow him to stand for about 15 seconds so he can "comprehend" what he just did. Then ask him again.
When he gets quick and consistent in his responses to a very small amount of rein pressure, start expecting him to give more before he earns his release. Just slowly increase the increments, making sure he is consistent at each "level" before you ask for more. Eventually, you'll be asking him to give his nose all the way to the left stirrup for his release. And naturally, he should also be standing still when he does this because he will learn you are not asking him to move his feet, but just to simply give his nose to the pressure.
Of course, work both sides (right and left) evenly.
To keep him from anticipating the direction, you can ask him to give to the bit on the left side while you are standing on his right side (for example). Just reach over the top of him to put pressure on the rein on the opposite side. This usually works easier once he understands that he does not have to move his feet for this exercise, so you don't have to try to avoid getting your feet stepped on while reaching over him. And this exercise usually confuses them right away because at this point, they've always been giving to the bit on the side you are standing. So that's why it is good exercise to follow the cue.
Once he knows this concept from the ground (and it may take up to a few weeks -- it really depends on the horse), then you can do the exact same thing from the saddle, starting just standing still and starting by just asking him to give a little bit.
The most important concept here is that you must release the pressure immediately when he gives to the bit. If you do not do this at the proper timing, he will not get a reward and he will learn to brace against the bit or ignore it competely.
As you are doing these exercises from the saddle, you can also be doing leg cues at the same time so that's he's learning them along with the rein cue (so then we are expecting feet movement if we are giving a leg cue). For a left turn, you'll do your regular direct rein pressure on the left rein. At the same time, make sure you keep your left leg OFF him, while applying pressure with your right leg slightly forward to "push" his front end over to the left. As always, once he turns the amount you want, you need to immediately release the pressure. Start with a small amount, and work all the way to making a 360 degree turn.
It's all about being consistent, releasing pressure at the correct moment, and gradually building your way up.
And it can never hurt to go all the way back to ground work bascis in order to fix an issue like this.
Being sassy is not an excuse. Ever. You are the leader in your team and you need to stay persistent and never stop cueing him until he gives you a proper response. Even if you have to sit there for an hour with the exact same pressure. You don't stop asking until he gives you the right answer. Don't ask "harder" -- just be persistent.
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It is not enough to know how to ride; one must know how to fall.