This is a voip number used by IC Systems, debt collectors for medical bills and other debt.  Their webpage is http://www.icsystem.com .  Their headquarter address is 444 Hwy 96 E, St Paul, MN 55127.  Send a paper letter via registered certified mail, listing your name and phone number, asking them to stop calling you at that number and to correspond via paper mail instead.  Keep the return receipt and a copy of your letter.  If they continue calling you again after 30 days, take your phone records, letter, and return receipt to an attorney (a bankruptcy attorney should be capable), and sue them for violating FDCPA.  They have a right to try to collect a valid debt within the framework of law, and you have a right to collect punitive damages should they violate that framework.