I was so shocked to find a 'BAD DEBT' report from NCO Financial Systems in my credit report. This questionable collection agent reported it to Experian, Equifax and Trans Union. And it had negatively affected my credit score. NCO never contacted me about any debt or collection (and I have not changed address for three years). When I tried to contact them by mail, their address was no longer valid so my letter was returned to sender (me).
Now I don't know how to contact NCO Financial Systems.