If you have an excellent payment history, you may be able to give them your explanation and ask for the late charge to be waived or reduced this time. Friendly reps may be amused by it 
I recently paid $20 on a $30 balance... just my typical payment not realizing I only owed $30. Next month I get a late charge of $27. Turns out my minimum payment that month had been $25, and since I only paid $20 I got charge the fee. I called and was nice and reasoned with them... come on... charging me $27 on a $10 balance? Really?? They reduced it to $13. I still think they could have given me a pass on that but I took what I could get.
I recently paid $20 on a $30 balance... just my typical payment not realizing I only owed $30. Next month I get a late charge of $27. Turns out my minimum payment that month had been $25, and since I only paid $20 I got charge the fee. I called and was nice and reasoned with them... come on... charging me $27 on a $10 balance? Really?? They reduced it to $13. I still think they could have given me a pass on that but I took what I could get.
I am so scrupulous about paying on time and avoiding interest fees. I had written the check, included the bill, sealed and stamped the envelope. I almost felt like crying.
That kid always could make me laugh.
