When working with the horse and a difficulty in arises in a movement or a figure, it is not a time to attack. It is a time where gentleness needs to be applied. Slow down and break the exercise into smaller parts.
Reward effort and do not concern yourself with correctness or results. Correctness is a matter of mind long before it is a matter of body.
Understand that any resistance which arises is the result of physical difficulty or fear. Aggression in such situations is not useful. It only justifies the resistance in the horse’s mind.
It is far better to start by assuming that the problem is in your aids than to blame the horse. Simplify; all the basic movements can be achieved on one aid
For movements at the highest levels (beyond Olympic level) two or three single aids may be cadenced and joined is a simple way. If you cannot get that to work then the fault is in the simple movements. Everything is in basic work.
The primary aid (single aid) in classical riding is always the hand (according ot de La Guéinère, who wrote the Bible of classical dressage) all the other aids are secondary. There are 4 primary directions and 4 secondary actions of the hand and two auxiliary actions.
There is a bit more too for each has 3 qualities and can express 4 elements. Most of the real fine points are not spoken of as much as they are assumed and intuited by the rider. To keep it simple one only needs to assume 4 primary and allow the 4 secondary to do what happens naturally.
The legs are used mainly for soldier who do not have the tact, education, or experience. This is the same reason the legs are popular in modern riding culture.
The seat is always a compound aid whose only real power is in an educated horse/rider. The seat is for blending the aids. Its main function is accompanying the horse’s movements.
Of course, this can be very confusing without education, but it is what it is not because I say so but because this is the way high level instruction works. It is rare to have the privilege of such instruction so the end result is a lot of confusion.