Got a collection letter

I have purchased a hosting/domain package from 1&1 last year. They apparently bill half of the package every 6 months, so they billed my account last year and they have tried to bill it again this February. The transaction was refused by my bank (not sure if it was due to funds insufficiency or some other reason) but nevertheless I have never received any communication regading the payment issue. Up until today when I received two separate letters from NCO Financial Systems, collecting $42.89 on behalf of 1&1. I called 1&1 to ask them what is the situation and they have told me that they tried billing me, the transaction was refused and they have emailed me an Invoice. I never got the email, the payment was not received so they have sent the debt to the agency.

I have canceled the account with 1&1
I have also prepared a DV letter I am ready to send it tomorrow

I pulled all three credit reports today and I noticed that there are no collection records on them. Is it possible that they are waiting for the 30-day period before they actually fully surrender this to the collection agency? Should I just pay to 1&1 instead and hope that they will drop it or should I proceed with the Dv letter? The letter reads: 'The named creditor has placed this acct with our office for collection. It is important that you forward payment in full. If you choose not to respond to this notification, we will assign your acct to a collector with instructions to collect the balance.'

Does that mean it is not fully in the hands of NCO yet?

And also, I have a question about the adress I should send the DV to. This is the adresses I have on the notices:

po box 15630 dept 99 wilmington de 19850
507 prudential road, horsham, pa 19044

I also called and asked where should I send letter and they told me this adress:

po box 15740 wilmington de 19850

And I also found this adress on the net:


6324 Fairview Rd, Charlotte, NC 28210