Perhaps you might like to use bind as a caching nameserver for your hosts use instead of service provider's dns servers?
May help with name resolution etc, if you do RBL lookups on incoming email, eg using spamassassin, and your dns request goes to your provider, you may find it gets blocked due to oversusbcription from host provider. Smaller volume requests from your own server may not be.
You might like to consider leaving named running, perhaps untick it in ispconfig. If you wanted to revert any settings possibly made by ispconfig, do a "yum reinstall bind" and if it creates /etc/named.conf.rpmnew from that install move it to named.conf. That way you have a stock install of bind as a caching name server which only responds to requests from the loopback address.
Check your /etc/resolv.conf and make sure you have
then your machine will use localhost for name resolution.
Finally, in your firewall block incoming dns requests (udp, tcp port 53) from the outside world.