That's just weird. I think I would call the mother at a time when I knew the child would not be with her. I would tell her that, while you care about her child, due to the circumstances that
she created in the past, you are not interested in having any kind of relationship with the family (either personal or professional). I might also shame her a little bit for creating a situation that hurt you and hurt her child. In a caring way, of course
.