Problems with blocking IP addresses

Hello, Our server is having issues blocking access to users from the following IP addresses: . We have added the three to the blacklist in the affected account using the IP Blocker in cPanel, but the users from those IP addresses are still able to visit our website and submit spam user registration submissions using a WordPress-based form. The WordPress site is using the Network multi-site setup and only one of the four active sites is experiencing an abundance of spam registrations from offending IP addresses. Does anyone have any suggestions on why this is not working? Cheers, -blocked-ip-addresses.png">67501