The IRS letter explains why it is being sent and what you should do (if anything). It should also have a phone number for you to use if there are any questions.
The LTR 673C is usually sent because the IRS received more than one tax return for the same tax year from you or an incorrect tax form was used or checking an incorrect box on the form.
Did you file a return and then mail in a corrected return that was not on a form 1040X?
No I called the irs and they said that it wasn't meant to be sent but that doesn't make since
Mistakes can happen ... so if they say it was an error and to ignore it then do so. It is possible that a paper return was filed and the data input operator entered the wrong SS# when processing it and it just happened to be yours by mistake ... another good reason to efile a return.
Contact the IRS, and request an Account Transcript. Compare this to what you intended to file.