CID "Unavailable"

Got a couple calls in a row, but caller did not leave a message.
I called them back and got an automated system.
Press 1 for more information, enter your phone number and someone will call you back for the organization they were calling on behalf.
Press 2 to be placed on their do not call list which will take 72 hours to take effect, then enter your phone number.

I've been getting multiple calls per day from this number for about a week.  Answered once nobody responded, been ignoring them (or trying to) ever since.  They call as early as 7:20am and as late as 10:30pm

they keep calling me and hanging up at odd times.

They call me twice a day. But I let it ring. I don't answer strange numbers.