I would phone the seller and advise that it was never received. Let them track it down or send a replacement. If they refuse to do so, presumably you paid with a credit card (just one more reason never to use a debit card),and you can advise your credit card company that the merchandise was never received. At a minimum, they will place the billing of that item on hold.
As to the USPS, that is quite a coincidence of not receiving two packages within a short time period. I suggest you send a letter to your local postmaster. I suspect they have a problem with the substitute letter carrier.
A while back, a woman rang my doorbell. She had a pile of mail for me, some dating back nearly one year. The house next to her had been vacant but she noticed that mail was being dropped off in the street mailbox on a regular basis. She decided to look inside the box where she found it nearly full of mail addressed to other homes. She took it all out and delivered it herself. I never did find out how or why that was happening. It made me double my efforts to make sure that all mail of a confidential nature was changed over to email delivery wherever possible. You can have just about all of your financial and billing account mail delivered via your email address.
She (local postmaster) basically said I’m SOL as the sub swears he/she delivered it.
I have seen comments suggesting not using debit cards on purchases in case disputes arise because there would be no recourse. I find this completely erroneous based on personal experience.
Just in recent past (2013 Christmas Season) I had two situations involving debit card purchases. One was on an account using Visa and the other, using MasterCard.
In both cases after I made a claim at my bank, my funds were refunded after a brief investigative period.
Perhaps the problems arise when using an ATM or Cash Card not going through the Visa or Mastercard processing network.
Not all debit cards are the same.