I'd pay it off if I had the money....
But, we got the same notice in a separate letter, but the letter was four pages full of legal gobbledy gook that took me 20 minutes to read through before I caught on.. Same as you, great credit history and suddenly a huge rate jump. But, when I called and raised cain they switched it back and credited me the increased finance charges. I don't know why.
But, I look at ALL of my bills. The mortgage company tried to tack on new charges for "processing" and increased my escrow amount saying that they were "anticipating" a tax increase at the local levels!
I was NOT successful in fighting that one. I got the extra charges taken off, but I cannot fight the escrow increase.
I said, "Dang the least you coulda done was buy me dinner before you did me like that!"