Never answer, and when you call back, there is an automated message stating that all circuits are busy now.

got a call from this number, and they left no message.

Who is the company that do this? All times hours, my private, unlisted telephone number rings? How so??

These calls continue to persist, for me as well, despite being on the DNC List. There is an APP on the iPhone, that, in essence, is "Call Blocking". You can take this number, and "Blacklist" it, so that your iPhone doesn't even bother to tell you this caller is calling. It might be worth it to upgrade for this very reason. Leave it up to Technology to find a solution that otherwise doesn't get resolved.

-ATG

Me too. They hung up as soon as I answered.