Chase did the same thing to me a few years back. I was able to speak to a manager and she agreed that due to my payment history, she would delete the late charge and reinstate my old interest rate.
I agree with others, that it's better to either pay through online banking (only if they pay electronically), or through the CC's website. Maybe you could use that to your benefit? I'm sure the holiday mail has slowed down a lot of letters.
Chase (and others, I'm sure) will also periodically check your credit report (Which I am FIRMLY against) and raise your interest rate if they consider you a credit risk, i.e., credit cards with high limits, etc., EVEN if you have a perfect payment history and regularly pay higher than minimum payments.
This happened to me. I used two credit cards, instead of taking out a business loan, because the interest rates were lower. BIG mistake. Chase made me so mad, that I paid that one off within months, just to prove my point... as if they care.
They send out a letter warning you that it's going to happen, but the letter looks like so much other junk mail that you get. If you fail to "opt out", you're stuck with the new rate. Just another sneeky way to get you. I'm sure it's all there in microscopic print somewhere on your contract, but I still think it's wrong. It's like biting the hand that feeds you.