So there’s a site that is bot-scraping Archive of Our Own (AO3.org) for fics, uploading them as PDF’s and selling them (I could be wrong on that, someone feel free to correct me). They have a DMCA take down page which is BS, and has language to make it seem like you need legal assistance to get your works taken down.
Many folks over on tumblr have seen their works there, including yours truly. This post has great info on how to get your works taken down from the site, including sending a notice to their hosting company and their Info page instead of their BS DMCA page.
AO3 is aware of the issue as well, as noted in this tweet reply to a user who pinged them.
So if you see your works, please contact them and request your fan works be removed from their page.