Sucks to have a post office where they don't care/have an attitude, had a spell back in the 80s with something similar where I lived at the time. Are USPS employees still considered government (ie-civil service) workers who are almost impossible to fire once they attain tenure?
Thing is, at least in theory the USPS must deliver to all addresses by law, where a private delivery firm can cherry pick profitable routes, and that is one of the albatrosses around their neck. I have never seen an Amazon delivery vehicle, their deliveries here are all via UPS or USPS. Not sure where the nearest Amazon warehouse is, but the nearest return address on any Amazon package I've received has been from Stoughton, Mass.