How do I completely block port using firewalld?

The way I solved it is I added a rich rule in the trusted zone:

rule family="ipv4" port port="6" protocol="tcp" drop

From what I know, rich rules are applied first. It seems to be working correctly in my case.

Some generic command are below

firewall-cmd --list-ports
firewall-cmd --get-zones
firewall-cmd --zone=public --add-port=5000/tcp

#Updated the url Aleksandar Pavić reported, Thanks Aleksandar Pavić

For some more docs and more details, please check it. https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/security_guide/sec-controlling_traffic#sec-Controlling_Ports_using_CLI