I seem to have an opposite problem, one of my packs was refunded with no notice from Epic or the buyer to give me a to fix the situation, obviously I feel quite bummed out about it and no clue as to what was wrong with my product, so how do I fix it from happening again? Now I feel some person has managed to get the assets for free and could easily pirate them out, I have no clue who bought the pack to begin with as we do not receive the buyers details.
I think the best course of action is to first speak to the owner of the pack and give them a deadline to respond and a to fix the problem first, CC Epic in. If the pack owner does not respond or does not attempt to help you I’d escalate it to Epic with your evidence.