They sent me this:

Response:
Shawn Green
Circulation Director
Harper’s MagazineDear Shawn:
Thank you for your recent letter.
Of all the people who regularly write me to ask about the money I owe them, you have the nicest manners. You don’t even mention late fees.
I commend you and your magazine, and enclose a hefty $19. Please consider my leap to an 18-month subscription an endorsement of your graceful correspondence.
I regret any concern my silence may have caused you.
Sincerely,
Kate Golden