I would cancel the cell phone...If that's her life line, I would snip it.
Can I just chip in quickly here, with a thought I had on reading this?
This sounds a bit like doing something out of anger, or at least a desire for tit for tat.
To me, this is getting caught in a dynamic where there is someone else involved (and that someone else is her). So your focus isn't on yourself with that train of thought and that action. You're doing something to get back at her for what she's done to you. You're not detaching with that (as I see it anyway, but I may be wrong).
I actually agree with not paying for her phone any more. But it's because she has chosen to turn away from you and the M, and has decided to focus her attentions on a new R. And as a result of that, she does not benefit from anything that you would be sharing with your mate: your bed, your closeness and intimacy, your attention (beyond the attention you would give a neighbour), and all the little things you would do for someone you were especially close to (cooking surprise dinners, washing, buying little gifts and treats, paying for stuff to make her life easier).
But none of that is done out of anger ore a desire for tit for tat. It's done because essentially the focus is now on yourself and on living your own life.
Forgive me if I've gotten details of your sitch wrong, or for anything I've said that's out of place.
