I think that is difficult completely to block all these from their IP address because they also generate another IP address to register on your site.

Perhaps you can consult with your webhosting provider regarding this and see whether is there any other method to handle this?

Or you can try block their IP address using .htaccess , you can refer on this reference link : https://htaccessbook.com/block-ip-address/

You can block them on different IP NO levels like xxx.xxx.xxx.xx levels and goe from country to D, C networks also etc I also have limit some of the worst spammers China, Russia etc see also htaccess file you can use

Thanks for sharing ssnobben.