Thank you for all who have tried to help me especially Bullten. I found his advice on another link and was able to fix the issue with binding.
Just simply go to CWP panel --> DNS Functions --> Edit Nameservers IPs --> then press Save Changes to rebuild DNS records
Then in SSH, this command now works:
$ systemctl restart named
However, I have another issue. Because this ticket is too long, I will open another ticket.
Many thanks again for this great community.
Cheers
Daro