Problem Iptables length

Hi there, my problem is that I currently have a Centos server with IpTables and I am currently attacking from several IP addresses to a specific port and I want to block it. Try several ways and to be able to block it and the attack persists. The attack method is SYN flood and also RST, ACK. I already checked the length of the package to be able to block it and everything but I put the line and it does absolutely nothing.

https://imgur.com/a/owKHTAa#OBUl4ct