The same kind of thing is going on in the US. If you look in the local phone book, there is a phone number published there, but it actually connects with a faraway call center, where they are prepared to give you general information about postal regulations and procedures, but nothing specific about your local area, except maybe the hours the PO is open.

Of course the local PO has phones, but they don't publish those numbers.

In my last job, I worked in the mail room of a university. Every morning a postal delivery truck dropped off a load of mail at our office (which we then delivered to the various departments), and every afternoon they picked up a load of outgoing mail. Of course we knew the numbers of our local PO so we could coordinate deliveries.

You might try this: Try to guess which company or organization in your area sends and receives the largest volume of mail. Call them and ask for their mail room. Then ask if they can give you the number of the local PO.

But don't bother the postal employees with trivia. Don't ask when your package will arrive because they don't know. And be patient with them, because they aren't used to receiving calls from the public on this phone. If they help you, thank them sincerely.