How to block an IP using iptables
Get the IP of that hostname:
$ host hit-nxdomain.opendns.com
hit-nxdomain.opendns.com has address 67.215.65.132
Block it:
$ iptables -I INPUT -s 67.215.65.132 -j DROP
I don't see a problem with the rules. To block an IP address, you use
# iptables -A INPUT -s 127.0.0.100 -j DROP
If you are still able to connect from that IP address, then check with tcpdump, if you are actually connecting with that IP, or if for some reason (Proxy, VPN, ...) you are visible on the host with the iptables rules as another IP address.