"Honor their wishes. Do not contact them. Send a note to them every 6-12 months asking if they still want to be left alone, and honor whatever their answer is. If they request that their names be removed, take is as your responsibility to see that they are removed. They are adults and responsible for their own interactions with God. Let them make those decisions for themselves."
One of the most ironic things I can imagine is that when those who are assigned to Home Teachers request that they not be contacted, performing Home Teaching according to the PRINCIPLE of Home Teaching (being willing to do whatever your assigned families want of you) means that you not contact them. That's extremely easy to forget.