Ex is Sending Negative Texts to Son About Mother

My question involves a child custody case from the State of: Florida
Hello, my ex is sending negative texts about me to our son. It has been upsetting him a lot. My ex is telling him i am out to get him and that I am going to jail soon. (which is not true.) My ex has also been harassing me. My ex will then forward the texts to my son that he sends me. How can I stop and follow the custody order? Should I have it changed?

Change his cell number or block dads.