Left intimidating message, without identifying themselves. Here's what they left me: "This message is extremely time sensitive. The hotline to my desk is 614-347-0380. Don't disregard this message to return this call. Now if you don't return the call and I don't hear from your attorney either, then the only thing I can do is wish you good luck as the situation unfolds on you... good bye." They have called every day, even when I did answer, I said to stop calling and add me to your DO NOT CALL LIST. The message is robotic, so they obviously don't take my request seriously.
If you can do it, turn off the machine and hear nothing more from them. With enough attempts and failure to leave messages or getting an answer, they might drop your number from their list. The fact they're able to get something will keep them bothering you.