I am having this problem too, just got my 4th bill without the discount on it.  I did the black friday trade in deal with the pixel (not the xl).  The online chat representative told me to call in for help, and the guy on the phone said he would put in a Promotional Escalation form and that it will take 2-3 days for me to get my credits.   Hopefully this is true.  I contacted them last month when I didn't see the credit on my third bill, and they said it would show up on my 4th bill.  We'll see if this works.