Custom edits of /etc/fail2ban/jail.d/issabel.conf can be overwritten with an update.
It is better to create a new file called issabel.local
You can use iptables or firewalld. They both do the same thing. I think all you need to do in order to use firewalld is change the default ban action although I have not tested.
So create /etc/fail2ban/jail.local file and add the following.
[DEFAULT]
banaction = firewallcmd-multiport
banaction_allports = firewallcmd-allports
Also yum install fail2ban-firewalld if not already installed and systemctl enable firewalld, 'systemctl start firewalld