Daughter demands to go with friend and friend's parents, when told no, goes anyway.

Have you ever had a situation where your teenager makes plans with a friend and the friend's parents, but doesn't clear it with you first? Then when you call the friend's parents, you get voicemail and explain that your teen is unavailable and can't go with them. (My daughter (16) has been sick a lot and needs to be recuperating, but daughter thinks otherwise.)So here's the kicker - the parents then pick up the teen anyway. Wha?????The situation is exacerbated by the fact that her mom and I are divorced, and when I make a parenting decision my daughter doesn't like, she just goes to her mom's.If that were just the extent of it here, then it's between her mom and me. But this is the parents of a friend!Am I crazy for expecting the kids' parents to honor my request? Aren't plans of kids under 18 between the parents of the kids (at the request of the kids)? I am thinking my ex told them to ignore my request. Are they being put in the middle? By whom? The parents are fairly decent people (although quirky). But my daughter is really the charmer and can persuade people quite well. How do I handle this?*EDIT This is actually the second time this has happened, the first time a few months ago I told the parents in a text that she wasn't being allowed to go, but again got picked up anyway. I did not address with them then, but I think I need to now. via /r/Parenting http://ift.tt/2p5a3rS