Someone with access to that router accessed it thru the internet just as you did and they set up the Mac filtering..You have to manually enter every mac address of every device that is running on your network in order to block Just one Mac address or multiple addresses..Then you have to set what mac address to block and save those settings just as you did to unblock your mac address on that specific device...Maybe someone doesn't like you having 3 devices on their network....Hope this helps

Someone with access to that router may have accessed it through the internet just as you did and set up the MAC filtering. You have to manually enter every MAC address of every device that is running on your network in order to block just one MAC address or multiple addresses. Then you have to set what MAC address to block and save those settings just as you did to unblock your MAC address on that specific device.