To ensure that the collection agency’s calls stop, you must give the collection agency written notice stating that you refuse to pay the debt, or requesting that the collection agency stop all further communication (a cease and desist letter).  In your cease and desist letter, it is helpful if you provide the telephone number for a collection agency to remove from their database.  Send your request via e-mail, facsimile, and certified mail so that you can maintain a record of receipt.  Further, a collection agency is required to investigate any claim that the debtor has been misidentified, the debt has been paid, the debt has been discharged in bankruptcy or any other reasonable claim that the debt is not owed.  A collection may not continue its collection efforts until its investigation is completed (i.e., the evidence of debt is obtained and the validity of  debt and contact information for the debtor are verified).  You may also contact the Federal Trade Commission (FTC) charged with enforcing the  Fair Debt Collection Practices Act which similarly to Arizona law, prohibits debt collectors from using abusive, unfair, or deceptive practices to collect from you.