Correct. Big free relays are their go to relays. My suggestion was in a hurry and is probably not that effective. Using WoT relays might be a way to go.

I also noticed they are posting their spam to other services not just the one I posted.

I removed relay .damus and nos .lol from amethyst.

But I'm seeing their post on other relays as well.

For the time being, be careful where you are opening nostr social clients 😄 the heavy lifting to fight this is in relay operators hand and us reporting explicit content if your client supports that.