Hi Kelsey,
Yes, this is extremely frustrating.
1. You can't communicate effectively with your ex-husband
2. Someone else, is interfering in you and your ex-husband communication.
Unfortunately, this is a very common situation. And there are different explanation for that. Maybe he is trying to avoid any confrontation with you. Maybe his girlfriend is a control freak and want to make sure you guys don't keep a good relationship (competition). Maybe talking with you is awaking some pain, fears, emotions... Or other.
What is certain is that he is stepping away from HIS responsibilities.
Legally, I have no idea how to proceed and what are your rights to make him discuss with you.
I have had the same situation.
During and right after our divorce, it was extremely difficult to discuss with my ex-husband. Especially on my side. He has been so mean and aggressive during the divorce. Didn't hesitate to lie to get what he wanted. He has said things that hurt me deep. And then acted like nothing happened.
He has been controlling and manipulative for many years with me and it has been difficult to get back on track and be myself again. Back then, I was destroyed, on the ground.
It took me a long time before forgiving him and accepting to pass all of this pain and bad memories.
Now, we are not the best friends but we talk.
It is important for me as our kids is OUR responsibilities. They need both of us and decisions regarding the kids should be taken by us and no one else.
Now, I know that his girlfriend is always taking the decisions (background) but she never dared interfering directly between our communications.
Maybe having a discussion with the girlfriend would be beneficial. Making her understand that you are not interested in coming back to your ex-husband but you need to exchange with him only regarding the children.
That instead of taking the decision yourself, you want to include him.
I don't know, these are assumptions. I don't know much about all the situation.