New spamusers on membership when i allow the registration at settings page.

Hi! Good morning.
I'm having a terrible problem, everytime i open registration i get a bunch of spamusers registereds. Also they know the invitation code and join right to the membership i've made and this is a lot disturbing, coz if they can get this information i feel like they can get anything from my website.

I've installed the IP Geo Block plugin to try to minimize the problem but had no success.
Now im only allowing these countries to view/access the website: BR, US, GB, AR, PT, CL
I did it coz it was showing some good information bout how was trying to access:
So, let me know if you need me to disable this plugin.

So, you will think something like this: "but if you're allowing the registration its good have new users, right?". No, its not. I have a Lineage 2 Clan website and i only want my members from in-game to have access.

Heres what is happening, yesterday i've created the user "art" and today all those new users were registereds and also them all are in the unique membership-nonpublic i have. As the picture bellow.

Need some help.