I think it may also be that you expect her calls to make you unnerved and so they do. Staying calm I think is the most difficult thing when talking to ex because even though they say they don't want to start a fight before they say something, you know that is exactly what they are trying to do.
If you know your ex is always go to see you a certain way, perhaps you could think of some calm replies and practice those. It's the idea from when I was a flight attendant, you practice for the emergency but hope you never have one. You also have those actions and drills so practiced that they come without much thought.
Just an idea and I hope it helps.
kat
Me-53(and learning!) S24, S21, D18, D17 Just keep swimming, Just keep swimming. Dory