I am sorry you had to go through this. I think I would have handled it the same way as you (although inside I would be deeply hurt). To me. the “when they go low, we go high” Obama quote comes to mind. And I think it’s the approach I would look back on and regret the least in the future. But I probably couldn’t resist a bit of a passive-aggressive move: I would thank the person for commenting AND for taking precious time away from his or her busy schedule to formulate a letter that must have been so difficult to write. Too much? Yes, I thought so.