I called *4637 and also 877-227-5511 (CBP). The helpline has been shut down, and the voice message directs callers to the CBP website. I checked my TTP dashboard and the green card is still there. Finally, in my original post I said that I had asked the officer to purge the green card info, but he said he couldn't do it for technical reasons (not on that particular day, but in general).