Fortunately, mine has not tried to contact me directly. She makes me fear for my personal safety and my career (based on specific threats she made). If she did directly contact me, I think I would respond with a more elaborate version of the following: "I am too in love with you still and it hurts too much -- I simply can't bear to have a more active role in your life at this time." I worry that not responding to her might not go over well. If I can convince her that I'm in love and that she has power and control over me, I think that will go over best.
And I don't see much point at all in pointing out anything I'm upset about with her -- she is not going to learn and it's not going to make anything better. In some sick way I think it would be rewarding for her if I lashed out with negative attention. If she begged for help and said that I was needed as part of some therapy process, I might consider helping in this context after at least a couple months of thought about it (at which point she'd probably have forgotten about the request).
I am in the exact same position, she call child services on me to try to get my children taken away so I do not want to give her the opportunity to do worse! I know her, I know this relationship was meaningful to her, I know I was good to her, and I want her to know that it is her that is the reason why I cannot be involved with her any more, basically either get help which I have told her to do along time ago and would not bother repeating, or stop sending letters and calls and texts and emails!