I'm so frustrated

I admit it I do a lot of ranting on here, but this one is legit. I'm very frustrated. DH's ex now can't seem to take the youngest to her dance class, a 1/2 hour class on Saturday. Granted it falls on her time as well as ours, but this is not about the fight between DH and his ex, the kid should be taken to her dance class. I am just so sick of these stupid tricks, why can't we all just act like adults and think about what is good for the kids? Also, we didn't get but 2 phone calls this whole week, we were supposed to get about 4, I mean what would it hurt to let the kids call their Dad? Would her head explode in flames? (well we know what I mean). I just kinda feel like we are dealing with a stubborn 10 year old that we don't have the right to punish, and we all know that the law doesn't seem to punish adultery or lying, things that in a just world she would be accountable for. She actually had the nerve to tell him the youngest didn't want to go that she was kicking and screaming not to go...funny when she is here, she never kicks and screams let alone says she doesn't want to go to dance. What little girl who dances at every turn, doesn't want to go to dance?????????? I wish there was a way to get less frustated...anyone have any tips? How to deal with stupid ex's?????? without resorting to violenc?????