Haven't seen in on mine either (yet), but I haven't seen the latest bill yet. I got mine April 14th (I think it was).
My bill hasn't been updated yet, but my current account balance has and it looks like the credit wasn't applied as my balance is about $100 more than normal (the Lumia $100 hardware cost I assume). I should have the bill updated soon and I will verify (and call CS) then.
My credit wasn't on my latest bill (which I paid this week), but I now have a credit on my account of $113 so it has been applied.