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You should be able to do this through the User Profile MAC Firewall. You'll want to make sure you're using the From-Access field> The Source MAC is the MAC you are trying to block> Set the Destination MAC to "any"> Set the action to Deny. Once you save this you'll want to make sure your default action in the MAC Firewall Policy window is set to "permit", otherwise you'll block traffic you aren't trying to block.
If this is how you have it set up and it is still not working, you might want to contact Aerohive Support (support.aerohive.com), or I know that most network firewalls have the capability to block specific MAC addresses as well.