I agree that a follow up email asking about the difference would be a good thing to do.
Question for you. Did you do the NPC before completing FAFSA? If so, can you go back to the NPC and do it by using your FAFSA SAI? That is, assuming the NPC will allow you to enter the SAI rather than manually entering numbers. It’s quite possible that the actual FAFSA information differed enough from your NPC inputs that it made a difference in your aid. If you get the same result using the NPC by telling it that you completed the FAFSA & entering the SAI, you definitely should find out why the aid didn’t match the NPC.