It seems that involves several different IP's . I would either check if there is a website using that service like a RES API or API connecting to one of the website for a certain functionality . If not then you may need to block each individual IP that connects from there from your fail2bann service in aapanel.
You can do that from fail2ban-> black IP. And add the IP to the list then save.
To obtain the IP you can use a DNS checker tool or ping it like this
$ ping ns3047305.ip-51-255-83.eu
PING ns3047305.ip-51-255-83.eu (51.255.83.123) 56(84) bytes of data.
64 bytes from ns3047305.ip-51-255-83.eu (51.255.83.123): icmp_seq=1 ttl=56 time=41.4 ms
In this case the IP is 51.255.83.123.
I can also suggest using firewall-cmd depending on your os. Firewall cmd is for CentOS
example:
firewall-cmd --permanent --add-rich-rule="rule family='ipv4' source address='51.255.83.123' reject"
Hope it helps