Do you have access of your cPanel SSH?
If have, try to use iptables and allow specific IP Address in INPUT that can access the cPanel then set INPUT to drop.
Kindly check the link below. Hope it help.
This method is very time time consuming. To enter each on individually could take DAYS.
So example here are just a few from Russia:
There is no way to delimit the IPs and therefore they have to entered individually, which could take DAYS to import.
There needs a better solution!