“And I'm not proud of my address, in the torn up town
No post code envy”

Lorde – Royals Lyrics on LyricsMode
It means that she doesn't care where she came from. Just be happy.
She comes from a poor part of town that is very ghetto.
Singer was born in Devonport. It is a suburb of Auckland.
New Zealand uses four-digit numeric postal codes.
The first two digits specify the area, the third digit specifies the type of delivery (street, PO Box, Private Bag, or Rural delivery), and the last digit specifies the specific lobby, RD (rural delivery) number, or suburb.
So. every city has its own index.
But under the new system, some suburbs in Auckland, Wellington and Christchurch now either have their own postcode, or share one with fewer suburbs.
She is not proud of the fact that she live in the suburbs, and it is seen by index.