Here are the list of the possilbe fixes.
1. I never believe his words. (don't use never and whatever together)
2. Whatever he says, I don't believe. (whatever is too big to be in the middle of a sentence)
1. I never believe his words. (don't use never and whatever together)
2. Whatever he says, I don't believe. (whatever is too big to be in the middle of a sentence)