What should I do when I experience inner denials, insults, and curses against the Divine Being, the Messenger, and his wives, accompanied by internal whisperings that describe some religious rulings as "superstition" and push me to insult and accuse others of lying, sometimes making me feel as if I have disbelieved?

The voice you hear within you is a waswas (whispering of Satan), so ignore it and do not pay attention to it. These waswas will not harm you as long as you strive against them and seek to get rid of them. There is no cure for these waswas except to disregard them and not pay attention to them. You must ignore these waswas in whatever form they appear. Cracking knuckles is among the disliked acts in prayer (makroohat al-salat), but it does not invalidate it unless it is done excessively.