The 'unstable' hierarchy is a meritocracy: the stable one is something like Socialism or Communism IMO.
In a society driven by socialist ideology you may as well ignore the lower status people: your masters are the important ones. Your performance is not important
In a meritocracy (on the other hand) its important to maintain and improve your qualities and talents.
One of these models produces a society that works.
The State enforces a stable hierarchy.
That is why employees of the Post Office disregard you - you lack status within their hierarchy. If anything at all, you are the Enemy, the existence of which is the basis of every state.
Just be glad that they aren’t as armed as the police, at least for now.