Horses are exciting, and frustrating. Sometimes it seems that they read your mind. Other times, well, it seems you just had one of those "other" times.
The instructor does not know how to teach students to motivate a horse. There is a reason that horse was not listening. I certainly cannot figure it out from here, far away from you and the horse, but you might have a chance.
The first things to think about are pain, confusion and fear. Perhaps the horse's saddle wasn't right. Perhaps the bit was wrong. Perhaps your hands were telling the horse to walk or to halt. Perhaps the horse was catching glimpses of one of those invisible scary things that only horses can see. If I were betting on it, I'd put my money on Bad Hands. Lots of riders who think they have good hands really do not.
I think you need a different instructor with a different method and a different attitude. Where do you find one? Well, I'll tell you a story about my instructor.
My instructor was good at teaching people who already knew how to ride, but I was a total beginner. I needed someone to remind me constantly about posture, hands and heels. He didn't. He also tended to teach a group lesson at the SAME TIME he was supposedly giving me private lessons!
Anyway, there I was on Ditto, an adult rider on an old school horse, and things were not going well. The instructor was talking to a bunch of eight-year-old girls, and ignoring me. One of the girls, sitting on the rail watching her buddies ride, yelled to her friend, "Susie! Where are your heels?" I immediately thought, "Snezzy, where are YOUR heels?"
An eight-year-old girl was unintentionally being my very best instructor!
I've learned from books and from horses, too. It never hurts to read Xenophon. (Who's he? Look up his book "On Horsemanship" that he wrote a very long time ago.)
The lessons are there and waiting for you. Find them.