Sometimes you accidentally pressed wrong key like escape, you cannot stop it by moving the character. It is because some skills cannot be interrupted.
HOWEVER
You can stop any spell / skill by pressing "X" key on keyboard, make your character sitting on the floor. Spell will be stopped immediately if you still have 0.5 - 1 second casting time left.
I found it very useful if you wanna stop casting imbued ring / wand effect or even evac. Get use to it and you don't need moving in battle to stop casting.