How would you handle your child’s other parent if they don’t let you talk to them when they are at their house?

We do have court orders that state we are allowed as many calls as we want but when I say he doesn’t coparent with me, he doesn’t at all. He goes over there every other weekend and I don’t invade on their time so I don’t normally try to call unless it’s like a holiday. Recently my son has been trying to call me more often and if I don’t answer at that moment, they (his dad and step mom), don’t allow me to call back. They tell him that I’m ignoring him and don’t try to calm him back. It surprises me that they do that and I don’t know what to do or say. They are honestly so mean to me and so I try not to contact them at all if I don’t have to