Dust in 5s camera - No Exchange

I recently went back to an Apple store (Short Hills, NJ) to exchange my 5s because it had dust under the glass in front of the camera. After being told by an employee who helped me during my appointment that they would swap my phone -- the dust can be seen with the naked eye -- (and that the AT&T 32gb 5s was in stock) another employee came to "investigate" the matter. He clearly saw the dust under the glass of the camera but turned the camera on and pointed it at a heavily stocked wall. He "concluded" that the camera functioned well. He said they would not exchange it but since it was within 30 days of receiving it I could return it and "buy" a new one but in the middle of this process I was told that all stock, except the space gray, was out. What's my next step? When did Apple stop swapping warrantied phones with dust under the camera?