Package stuck in a small town, need some general advice on the situation.

I have like 150 orders this year and I've never ran into this somehow.

They told me they don't deliver to the address even though it's 4 blocks away from the USPS.

They kept referring to a PO box even though I have a house address for this order which I guess has something to do with how small towns process packages like this.

This is really frustrating and I can't get a hold of the buyer whatsoever.

I think I understand the process once I get it back, but how can I prevent this in the future? This is fuckin stupid I paid for delivery and they didn't deliver it.