I just went through this with my host and it took me a couple days to figure out what was going on.
I suggest you do the following:
Change your register.php by using this mod here:
https://vborg.vbsupport.ru/showthread.php?t=297834
I was getting slammed by Chinese IPs, (spammers,hackers) what ever they were over 1000 times per minute!
I also had to block a full range of Chinese IPs that were causing the issues through htaccess.
If you want to try it out I can give you the whole list of IP ranges that dropped my site's cpu resource usage down to what it was before.
But you definitely want to change your register.php to keep those spammers from hitting your site.