I have delivery confirmation but seller says never received item

[four.wards]

Hi all,

Wondering if someone to point my in the right direction to help resolve this matter with buyer.

I shipped an item using USPS on May 12 and it shows delivered with delivery confirmation on May 14. Buyer just let me know that the item was never received. See note from buyer below:

Thanks for sending me the tracking number for my purchase. I checked on the USPS website, and it showed as "delivered" on May 14. However, I have yet to receive this item.
I've checked with the front office of my apartment, and I've called the USPS to see if they could locate the package. The front office says they never received it. The mail carrier says he knows nothing about it, and when I called the USPS I never heard back.
Is there anyone you could contact on your end to try to run this item down?

Thanks,

four.wards

[four.wards]

Much thanks everyone. I spoke to customer service at USPS and they initiated a claim for the buyer (even though it shows delivered). I gave the buyer the claim number and told them they would have to follow up directly. Haven't heard back yet.