I see the difference being in the consideration given to whatever is rejected or refused. When something is "rejected", there is some reason. For instance, a product is defective, or they don't like you, etc. "Refusal" requires no reason whatsoever. The image in my mind is a person standing in front of you blocking your path, shaking his head, and saying "go away", but not necessarily for any particular reason. At least, that's my take.