While adding the devices in MAC filtering and the option which you are selecting as “Whitelist: device must be listed below”, does this option severs the access to the devices in the MAC filtering or to all the devices connected to the modem 

Thanks for the reply. When I enable whitelisting, access is disabled for all devices, including the devices on the list.

Also, why is there no way to add a label to the MAC addresses so we know which device the address corresponds to? Every other router I've ever worked with has that basic feature. With this one, I have to keep an external list of MAC addresses, which is ridiculous.