Used clothes, at least here in the north are called pèpè or maybe pepe. Do you know which?

It’s "pèpè".  They also call them "kenedi" or "rad kenedi"

They are more specifically barely used or second hand clothing (usually from the US) sold in the Haitian flea markets.  

We may say “rad drive” (rad dreevay) – when talking about used clothing we wear at home,  clothes not used for outings.  We also say “Rad ize” (“Rad dezyèm men”) – used clothing

Rad sòti – clothes used for outings, good clothes

Haitian Creole ↔ English Reference, Look up Haitian Creole and English Words