This happened to me in August. The due date was on a weekend, and I knew it was on the weekend and due to my own carelessness, I flat paid it 2 days late.
I got a $39.00 late fee and since I always pay my bill in full every month and this was 2 days late- they charged me interest. Now not only did they charge me interest on that month BUT they said I was still accruing interest even in the next month. This made no sense to me. If my payment was due on August 1st and I pay it August the 3rd- why am I paying interest the whole month of August??
They waived the $39 fee but said they would not waive the interest. Since I had the money to pay all along- it was a very expensive lesson to me to pay that stupid bill as soon as I get it.