I want to add to the good advice that instead of getting frustrated, you could make a fun detective game out of it: think to yourself, "How interesting!" when you & the horse don't have the same goal in mind. Horses are experts at frustrating predatory types like us humans, so he feels your frustration and chalks up a point for himself! However, amidst this,the horse is doing you a great service by showing you this, so please appreciate how much he's teaching you! That said, I have my doubts about your instructor, because surely, your instructor's seen your troubles in your lessons & has given you no help.