The same thing happened with some of my resources, which ended up on sites like Studocu and Course Hero. In my case, I don't really mind other people sharing my resources, especially since it means that they can potentially reach more students, as long credit is given, i.e. as long as I am recognised as the original author, instead of modifying the resources in a way that makes it appear that the poster is the original author, the latter counting as stealing.
If you do not want to have your resources published on other websites, I would recommend two courses of action:
- Check if you can contact the poster of a particular resource on the relevant website. If that is possible, inform them that you do not give them permission to upload your resources and request that they take it down. Give them some time after you contact them. If the resource ends up being removed, then great!
- If the poster is unresponsive/uncooperative, or if you are unable to contact the poster because the relevant website does not offer such a feature, you should report the resource. There are typically a number of reasons for which you can report a resource, one of which being that you are the author of the resource and did not give permission for the resource to be posted on that website. Hopefully, your request will be reviewed and the resource taken down.
I hope this helps!