Bank of America had a $30.xx on my account as an intesrest charge although I paid the balance in full and before the due date / closing period. The second service rep I spoke with removed the charge and apologized after the first one had no idea why it was there and had to transfer me. No one could explain the charge.
Make sure to check your accounts regularly.
I dont care for BOA in general but they currently have the best cash back CC, but if it happens again I wont hesitate to ditch them.