Sometimes it is not the bit that the horse hates but it is the strong hand of the riders or even maybe just because it is a school horse, he can have a reaction to different hand usage. If you can not do anything with the bit, try to figure out how to use your hands as the way he accepts by trying.
Chances are the horse hates bits because he/she is a lesson horse. People learning to ride rely a lot on the reins to keep balanced so I can see why the horse would dislike bits.
My suggestion is to talk with your trainer or the one that choses the bit.
Do a bit more of research on the bit you are using and on the bit you belive it is best for your horse.
Hope your question was answered!
Feel free to contact me!
By rights, you don't need a bit to ride a horse into an outline or school a horse properly. My horse is bitless & ridden in a rope halter, she's 23 & been bitted all her life, she hates the bit & she schools lovely in the knotted when her head is in the game. Although, we don't school in an arena very often due to her age but we school out on hacks. She leg yields really well, transitions, tracks & more even though she's not bitted. The world is slowly changing their mind on horses not being able to be ridden correctly if bitless. The only downside is, you cannot compete dressage bitless but you can Showjumping & I think cross country too, but don't quote me on that.
So, in answer to your question, learn to ride from you seat & other aids except the bit. It's an aid not a control device. Good luck x