How can I request a refund for an App Store purchase?

This morning I woke up and saw my apple email saying that i had bought $7 worth of robux on February 9th. On February 9th, I couldn’t use my debit card to buy robux , when I was buying robux it would tell me about my billing information and it needs to be updated. Now it’s currently February 17, and it charged me $7 from my bank.

[Edited by Moderator]