Perhaps it would help to keep the phone conversations limited only to discussion of visitation, and if he can't adhere to that, then end the conversation and hang up.
Fortunately I had no children with my EXAH. After I left him, he continued to call, which would leave me in a tailspin for days.
This was back before the days of caller ID, so I would answer the phone.
I started hanging up on him as soon as I heard his voice.
Eventually he got the message and quit calling.
You don't have to hear his excuses if you don't want to.