National Credit Recovery. Help Please?

In February 2010 I received a letter from National Credit Adjusters about a debt with Regency. Because I had never hear of National Credit Adjusters or Regency I sent in a debt validation letter that I got from this website. I sent it certified mail and they got it on 3-8-10. I never received any other information from them or heard anything else. Yesterday the state office of the agency that I work for got a phone call saying I had this debt and if I didnt pay they would garnish me. I pulled a credit report yesterday and it shows a collectioin account for National Credit Adjusters. How can they put a collection account on me, tell my co-workers about my debt and place a garnishment on me without even notifying me? I am at a complete loss. I do not know what to do next. Can you please help? Thank You.