But if I open the cli, and have a loock at fail2ban.log or auth.log, I see, that this IP still try to access the server. So it seems not to be blocked by the Firewall-Rule:
if you use firewalld, you probably should set banaction in /etc/fail2ban/jail.local or any custom conf, to some relative action. eg.
banaction = firewallcmd-ipset