Not really sure what's wrong, but try this:
1) Reset your modem/router
2) Type /version in-game and tell us what it says in the top-left, it should say 1104
3) In case the above does not work, try completely shutting down your firewall for a second, and check if you can see servers
EDIT: Another thing you can do:
Go to System Preferences > Security > Firewall > Advanced > make sure assaultcube is there, and that it is accepting incoming connections.
1) Reset your modem/router
2) Type /version in-game and tell us what it says in the top-left, it should say 1104
3) In case the above does not work, try completely shutting down your firewall for a second, and check if you can see servers
EDIT: Another thing you can do:
Go to System Preferences > Security > Firewall > Advanced > make sure assaultcube is there, and that it is accepting incoming connections.