Basically, they commissioned me last year and there were one or two warning signs, but I ignored this and completed their commission and thought that was done for.
I then noticed they'd reposted their commission to their account, which is something I'm fine with. My ToS states that the commissioner must credit me and only repost the lowres version of their commission (I provide a hires file with no watermark and a lowres file with a watermark for all my commissions). They ended up posting their commission to their gallery two separate times, the first with no credit and using the hires file, and the second with the lowres file but still no credit. I finally got them to follow my ToS after a lot of persistence, at one point they claimed they were too busy to credit me properly despite replying to my note immediately and screencapping their gallery to 'prove' they did in fact credit artists.
I thought this was the end but then discovered they'd reposted their commission to their Tumblr, again with no proper credit (I can't remember which version of the file they'd uploaded as it was a while ago). I ended up filing a DMCA as I did not want to deal with them again and Tumblr thankfully took the post down.
Again, I thought this would finally be over with but today discovered another Tumblr blog they'd created and had yet again reposted their commission, this time with no credit and using the hires file. I've filed another DMCA and am waiting for Tumblr's response as I write this. I should add that on both blogs they've reposted multiple other commissions and have credited them all.
What I'd like to know is if there's anything I can do to prevent this from happening again? They've proved they won't listen to me in the past so I'm not sure simply telling them not to repost again will work. On top of that they seem to have abandoned their FA and left it in the care of another FA user so I'm not sure I'd even be able to get through to them. It's getting tiring chasing them down across multiple websites as I'm aware they're on several other websites such as Weasyl and InkBunny, but don't seem to have reposted my art on those yet.
Thank you for any help you can provide!