Don’t know what to do

My ex husband and I finalized our divorce last September of 2022 and in our decree and parenting plan we have a agreement where he is to get our children every other weekend and every other summer and holidays and we both have joint custody of the children. However, he hardly gets them or ask to see them and only will talk to them if I call them and get the kids to talk to him. He is not following nothing on the parenting plan and never shows up for the kid’s birthdays or on anything he promises them he is going to do. And my kids always come to me disappointed until he ask promises them something else again and they get excited again. Just recently it was my son’s birthday and he promised he was coming on a trip to be there for his birthday and never showed up my son was mad at me and heavy disappointed and never told me why he wasn’t coming but called my son tablet and told him he would take him out this weekend and still hasn’t said anything. I don’t know what to do cause im tired of my children being disappointed.