Roblox is asking for an iTunes Receipt

My son's Roblox account was evidently hacked. He cannot get into the account, and we have contacted Roblox Customer Support. They have asked for an iTunes receipt for some reason. This is their verbage: "In order to verify ownership, please reply to this message with a copy of your iTunes purchase receipt for the iTunes payment made on your Roblox account. You may send us your emailed receipt or a screenshot of your Roblox, iTunes purchase history."

I am wondering why they are requesting this instead of purchase receipt from the App Store which is where we would have purchased the game. Can you help?