Future, with all of our opinions here ... I would take a week to just think about what you really want. Your W obviously doesn't want to talk right now and is avoiding you in order to avert doing so. She has been enjoying the status quo and probably doesn't want to change anything right now. I don't think forcing her to 'listen' via the letter is going to make her come home. You have to be prepared that this is not only the LRT, but probably the end. Are you ready for this?
If not, then wait another couple of weeks. Detach first. Drop that rope of hope. Don't speak to her about anything except the kids. In fact, if you can get a third party (a grandma, or aunt, sister, whoever) to collect them for you, even better. So, that you might stay away from her for those 2 weeks and see how you feel about 'no contact'. If she doesn't come to you, then write the letter (if you feel you must) and start separation process.
I think 'no contact' would speak louder than words about her disrespecting your boundaries. It will also give you time to think without seeing her for a time. (Obviously, no phone contact either.)
Just a thought.
Me:57 H:52 M:28 Got another lawyer last year and filed. D35,S/D twins28,D22 EA4/04 End? Who knows? "Life is like a mirror. Smile at it and it smiles back at you." — Peace Pilgrim