Can I get into trouble here?

Here is the situation: The father of my two kids' live in girlfriend has interferred with a dentist appt for one of our kids. She went behind my back and asked the dentist office for information on the child's record, and made an appt that I was in the process of scheduling, I had already informed the dad of our child's current dentist issue and that I would be making an appt. My ex did not know that she had gone to the dentist office to get this info and setup an appt. He is now protecting her and saying I did wrong. She said "I dropped the ball" on this. They are doenting as well as speaking to their attorney to file a contempt motion. I am the custodial parent with primary placement and the ex and I have joint costody. I did cancel her appt and reset the appt, I tried to call him to tell him of the new appt but he will not answer his phone, I dont want to leave a message either, I perfer to speak directly to him.