But to have a workaround on the first issue, I tried to add a custom Upstream DNS which is the OpenDNS Family Shield (208.67.222.123, 208.67.220.123). I have saved and restarted the dns service and even the system, but it still doesn't work according to opendns' test page.

How can I tell if it's working? (super noob) : pihole Sep 02, 2015 OpenDNS not working - Apple Community Jan 01, 2016

This all just started working. I have to imagine that the WRT1900AC had the OpenDNS servers IPs cached from the Comcast DNS servers during the first round of tests (which would be odd because I rebooted the WRT1900AC, which I woudl have expected to purge the DNS cache). So as far as OpenDNS is concerned this seems to be working (yay!). -MC

Testing WMI Connectivity with WBEMTest – Cisco Umbrella

flushed all cache and dns on all machines, waited a day or so, still the sites I have listed on the opendns account are not being blocked. Also on the opendns page I see an ip address of 208.65.149.242, but on the opendns updater (which I have on one pc on the second router/network), it shows ip address as 24.229.173.2, which is my providers' ip.

If you can access a website at office or from a 3G network yet it's not working on your computer, it is a good idea to use an alternative DNS service other than your ISPs. OpenDNS or Google Public DNS are both excellent and free public DNS services. [SOLVED] Checking if DNSCrypt is working / Networking