Because your behavior belongs to the right of visiting, no one can stop this right. Your ex-husband has violated your rights, so you can go to the court and continue to apply for enforcement. If he still won't let you visit the children at this time, then he will violate a greater right, and at this time he will arrest and detain the education.
And if he does this regularly, then our law will award the child to you, that is, you have custody, so he must enforce it.