How to stop Datapump Job

DECLARE

   n NUMBER := 0;

   errm VARCHAR2(2000);

BEGIN

   n := DBMS_DATAPUMP.ATTACH( job_name => 'MYJOB', job_owner => 'ADMIN_USR' );

   DBMS_OUTPUT.PUT_LINE( n );

   DBMS_DATAPUMP.STOP_JOB( n );

EXCEPTION

  WHEN OTHERS THEN

    BEGIN

       errm := SQLERRM;

       DBMS_OUTPUT.PUT_LINE( errm );

    END;

END;