Help! OpenDNS is not working with Asus rt-ac66u

Hi, i am using Cox communication, which has COX cable/router.

I am connecting my asus router to the Cox router (with default DNS), and have my children's computer and ipads connect to Asus router (with OpenDNS.)

However, OpenDNS is not blocking/filtering any adult contents.

Did the OpenDNS dignosis check, i do see "checks" and saying i am using OpenDNS.

I also run command in CMD

nslookup -type=txt debug.opendns.com.

C:\WINDOWS\system32>nslookup -type=txt debug.opendns.com.
Server: RT-AC66U_B1-1F78
Address: 192.168.50.1

opendns.com
primary name server = auth1.opendns.com
responsible mail addr = noc.opendns.com
serial = 1613772894
refresh = 16384 (4 hours 33 mins 4 secs)
retry = 2048 (34 mins 8 secs)
expire = 1048576 (12 days 3 hours 16 mins 16 secs)
default TTL = 2560 (42 mins 40 secs)

C:\WINDOWS\system32>nslookup -type=txt debug.opendns.com.
Server: RT-AC66U_B1-1F78
Address: 192.168.50.1

Any one know what have I done wrong?

thanks