More than once, I've had a package tracked as delivered when it really wasn't. The first time it happened, I called my local USPS station, and a very polite woman apologized and seemingly already knew what had happened (or she just had a generic reply that sounded feasible). She told me the mailman marked it as delivered before he exited his truck, but upon finding me not at home, did not want to leave it on my doorstep. Apparently there's no way to undo the marking of delivered. Sure enough, I got it the next day. A couple weeks later, the same thing happened. I didn't call, but it showed up the next day. I can understand that an urban mailcarrier would rather mark everything in his satchel before he gets out of his truck rather than carry his barcode scanner around with him to mark them as he drops them off.
Its slightly annoying, but I''m grateful for tracking in general, so I deal. Good luck! I hope you get it!