Strange, an ingame store definitely goes though their system. Did you send the proof of purchase to epic support? Considering they control your epic account they can adjust things on it.
That said, if you used the Samsung Billing solution Samsung could effectively refund the purchase... However, if that isn't done in agreement with epic your account will most likely get banned from fortnite (This will probably trigger automatically so its very much recommend to have a ticket beforehand ready at their side.).
