Contact
Write to contact@astrangersshelf.com.
That address reaches the person who runs the Shelf. There is no support team and no ticket number, so a reply may take a little while.
Reporting something you have found
There is a faster route than email.
Every creation has a Report link beneath it. That is the quickest way to flag something that breaks the Submission Guidelines, and it tells us which piece you mean without you having to describe it.
Copyright
If your work is here and you did not put it here, write to legal@astrangersshelf.com.
The Copyright / Takedown page explains what to include, and you do not need a lawyer to send it.
Taking back something you left
You do not need to write to anyone.
When you left it, you were given a private link. That link lets you remove the piece yourself, immediately. It is the only way, and it cannot be reissued — there is no account to recover it from and no email address on file.