I had a similar situation a couple years back-them calling from about 3 or 4 numbers daily. I rounded the numbers up and found someone in the local office who cared enough to help me and the next day the calls stopped.
Hang up call every day, never a response. I leave the phone off the hook and caller attempts to make other calls and can not. After a few try's the caller disconnects, and a telephone voice messages comes on.
Many calls from this number, "anonymous" on caller ID, no one on line (I do not say anything - I wait to see if there is a person on line vs.robo caller) and no message left.