Fail2ban is a daemon that can be used to monitor the logs of services and ban clients that based on incorrect behaviour.
A must have on your Linux system.
But sometimes you can forget enabling the correct jails, therefore always check the active jails on your system.
This can be done with the "fail2ban-client" command:
#> fail2ban-client status
Executing that will show you the list of active jails. Ensure that your jails are listed over there.
|- Number of jail: 5
`- Jail list: apache-modsecurity, apache-overflows, apache-shellshock, nginx-req-limit, sshd
Is your jail not listed? Ensure that "enabled = true" is set in your jail configuration.