Hi,

For your information, the device used to login to the web interface cannot add itself into access control or parental control list. Cause it was regarded as master/parental device. 

And we are sorry  to tell you that the blocked device cannot access the configuration page anymore, if you want to unblock it, you need use another device to login and unblock it.

It is designed to block internet completely, otherwise the device itself will login to the configuration page and unblock it to access internet. 

While if you add the device into parental control, select whitelist without any keywords and choose 24/7 as internet access time, even though it cannot login to the web interface, it still can access the devices in the same network.

May it help and have a nice day.