If she has just told you over the phone or email that she is denying your time, that's not enough to prove contempt. You need to physically go to get him and have her deny you then. Take a witness with you. Purchase something and get a receipt to show you were there. Take your court order with you.
If she won't release the child, have an officer make a report to that effect. Subpeona the officer to testify.
Next time, if she gives you more warning that she is denying, there is an "intent to exercise visitation" letter at
SPARC - Divorce and Custody Help you can edit and send to her, in which you quote your court order and pursuade her to cooperate.