Name servers
ns1.otherdomain.com (Points to: my public ip)
I assume this is the IP address of the server running bind.
How about a few sanity checks.
1. curl http://www.icanhazip.com and verify that you are using the correct external IP.
2. install chromium-browser. SSH -X to the server and run chromium borwser. www.canyouseeme.org will check ports on your IP. YOu can check port 53 to ensure it is opened properly.