1 800 553 7650 is for Elan Credit Services,  they use this number to activate your new card or to verify your information when you receive it. It is not a bill collector. If you have a new card, they also call to verify your phone is a working number.

This is a number for a credit card company to confirm you received the card or to remind you the bill  is due... I just got the card and now I have to call and confirm...

Just received a call from this number.  Didn't answer it.  I called it back with my number blocked and it said "Thank you for calling to active your card.  Please enter your 16 digit card number now."  I know there is no credit card with this number listed, this is an analog phone line I keep at my office to dial out when the internet is down.  It has never been used for anything else for 10 years.

From a google search on this number. I copied and pasted this result.

    
Track UPS package 18005537650
www.ups.com

They called again Sept 25th after having stopped calling for a while. Still bogus. Leaves no message. If it really was the govn't trying  to get past due taxes from me, I am QUITE certain they would leave a message.

Has called two days in a row now on my cell phone. Didn't answer, no message left, "caller unknown" is ID.

Through the power of  the internet and google I found the answer. The IRS Federal Payment Levy Program.

http://www.irs.gov/individuals/article/0,,id=100551,00.html

You'll find their number listed in the last paragraph of that page.

Am a little confused by the goven't jargon on the page, but it seems as if they are a part of the IRS that is trying to either collect overdue taxes from me, or arrange to pay me some sort of federal program payment....neither of which are situations that apply to me....(Though it would be nice if it was the latter!)

Got a call around 6pm.  Didn't answer, no message left, caller name blocked