Do you pay mortgage on the first of the month or just before the 15th (or before the late fee is assessed)?

[Charles Mangum]

My mortgage coupons state that the payment is due on the 1st and after the 15th a late fee will be assessed. I started to pay them on the 14th, however, I received a voice mail from the bank that the payment was late. Is this just a tactic to get me to pay earlier or is it actually late and could they damage my credit by reporting that my payments or late to the credit agencies. Getting an extra two weeks out of your money would add up over time.

What do you do?