Call the IRS between 7:00 and 8:00 AM in your time zone. When you push the buttons and it asks for your social security number put #0 instead of your social security number. That confuses their computer and sends you to the next available live person.
Any electronic transmission can have an error in it and not go through properly. Mailing would most likely be a waste of time. The IRS has trailers of mail in parking lots that they will take months to get to.
Sometimes they seem to hire people to answer the phones that don't know what they are doing. I just keep trying until I find one that does do what they say they will. It sounds like the problem is on their end. I would fax the form even if you are not on the phone with them With the fax include a cover sheet with your name and what is going on. Also fax a copy of the CP11 letter. Number the fax pages like 1 of 3, 2 of 3, etc.
