Put the errant mail back in the box and put the flag up.   Carrier should figure it out after a couple times, although I've seen a couple of carriers that are dumber than a box of rocks.   My own farm is served by a highway contract carrier who isn't a postal employee, she was just the low bid.   I'd say she ranks as the dumbest, slowest, most useless thing I've ever seen in the PO.  

Back to your problem, if it persists, give your postmaster a call.   No reason for it to keep happening, ASSUMING proper addresses are being used.