Didn't Receive My Item

[l8dglfr2012]

I received an email with an estimated delivery date for my pkg of 8/26. I did not receive it that day so I thought maybe it'll be here the next day. Again, no package so I looked for my tracking # and found that it was shipped by the seller on 8/21 and arrived at my local PO on 8/24 and delivered to my mailbox on 8/24. I did not get a key for the bigger mailbox where the package should have been. I went to my local PO with this information. They tried to notify my postman to try to trace the pkg, but he was probably at lunch and didn't answer. The PO said they would call me so I left my phone # with them today and of course they didn't call. I will go to the PO again tomorrow to demand an answer. I'm assuming that they won't find my pkg and want to know if I can get a refund for something I didn't receive. What happens if it is a delivery problem?