I had the same situation
This is what happened.
If you make a reques to INS, then INS will send you a duplicate AP notice. But, that notice will not have your photographs or anything.
So, it is absolutely useless.
My AP was lost in mail initially,but I found it in mail after 4 weeks or so. In the meantime, INS did send me a duplicate notice (which is no good) and also requested me to re-apply for the AP with new fees.
My suggestion is to wait for a week more and apply again (with fees) with a letter saying that the AP was lost in the mail.