It is Asset Acceptance Corp. (AACC) Or Unknown number, via caller Id.  You can not block these people!  They are in cahoots with your phone company.  They are Zombies, trying to collect on old written off debt from your long lost past.  Don't give them a penny or they will reopen a case against you. They buy old debt for pennys, beyond the statues of limitations, and harass you.  They use several phone numbers.  They will illegally destroy your credit by marking it with 25-50 dollar payments that you never made, so that they can get you.  Get lifelock for the credit, but be prepared for the hounding phone calls after you place an alert on your credit.  They need to be investigated because it seems criminal.

Calls 2 to 4 times a week. Leave long messages on answering machine