I sent them take down notices and persisted until they took my stuff down. It wasn't easy, took weeks, and really pissed me off, especially since I thought I'd been a bit daft putting one of the stories on Medium because I might have been able to sell it to a magazine. I then deleted some of my stories that had potential to be used in part or in full for a magazine (checking to see if they'd been plagiarised first) and I haven't put up anything that I might be able to use in that way since. Lesson learned.