A Validation or Two: What Can I Do Next?

[Snowdrift]

Hello all! I'm here to ask you please for some input on a recent collection attempt:

Back in late January '07 I received a letter from Nation Wide Credit referencing a debt from AMEX for $3000. I sent them a certified DV letter asking them to prove the debt is mine and to contact me only by mail, and they in turn sent me 2 envelopes with copies of monthly statements from account open to close. I haven't heard from Nation Wide since the day they sent me those copies.

However, I've been getting phone calls since February '07 asking me to call this number: 1-800-322-2608 and since I was sure it was NWC Inc. I called the number, and it answered as NCO.

At first I thought maybe they were an "also known as", but I see that they both have received hefty fines by the FTC:

http://www.ftc.gov/opa/1998/10/nationwide.htm

http://www.ftc.gov/opa/2004/05/ncogroup.htm

I did speak with them briefly, asking them they what they were calling me about, and they said they had sent a letter to my PO box but it was returned to them as "undeliverable." Since they had my correct address the only reason that I can think of that it would be returned was if the PO box was closed--but it's not, I pick up mail there daily. So it sounds to me that a new CA has taken the account and immediately started with the phone calls and bypassed a letter asking me for payment.

I am wondering if I should send Nationwide a second letter saying "it has been more than 30 days since I last heard from you; If I don't hear from you in the next 5 days I will consider this matter closed...." Is this called a "Second DV Letter" and does anyone have any examples I could look at?

Also, is NCO in violation of the FDCPA by not sending me a letter with the paragraph that states they are trying to collect a debt, etc. and starting immediately with phone calls? I'm guessing I should send them a validation letter as well.

I'm new to these boards and relatively new to dealing with collection agencies---so thank you everyone for your advice!