Looks like an issue with the printed bill, probably because it's your first one. I'm not a billing expert, but I belive your actual Due Date is January 1st.
It will correct itself once your second bill arrives. I'll escalate the printing error.
Thanks Alex! I phoned and they basically told me the same thing -- they wouldn't charge late fees if I paid by Jan 01.
But for all the stories I read here about various ISPs, it's exactly when the font line staff say "You have nothing to worry about." that it's time to start worrying