I have been awarded weekly unsupervised access of son - what happens if the mother still refuses?

As the court have said you have rights to see him, she can't stop you. She has no right. You could go pick the child up yourself from her place of residence, and if she doesn't show up to bring him to you, you'll need to talk to your solicitor so social services. Denying a child the right to know their parents is wrong, even if they're no longer together.