This is definately an AT&T issue. We have 3 different types of cell phones being used by my family and in my home, and all show these erratic data charges. It ould logically make sense to me that certain services must use 4G, however I am being charged during times that my phone is completely shut off, which is every night at 8AM, turning back on at 7AM. Reviewing my logs on a 24 hour rotation - well the answer still doesn't add up correctly. I have even tested this by turning my phone off for a full 24 hours and there are still KB times being charged to my account.
Try again AT&T or return our data back to us.