I am trying to block an IP address from accessing my server by using iptables, but didn't succeed.

Here are the commands that I used. (after these commands, I still keep seeing 50.18.12.86 sending request to my Apache server).

sudo iptables -F
sudo iptables -I OUTPUT -s 50.18.12.86 -j REJECT
sudo iptables -I INPUT -s 50.18.12.86 -j REJECT
sudo iptables -L -n

Chain INPUT (policy ACCEPT)
target     prot opt source               destination         
REJECT     all  --  50.18.12.86          0.0.0.0/0           reject-with icmp-port-unreachable 

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination         

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination         
REJECT     all  --  50.18.12.86          0.0.0.0/0           reject-with icmp-port-unreachable 

I have tried DROP instead of REJECT, but doesn't help.