Roblox Charged Me Twice - I Did Not Get My 500 Robux

I bought a 500 Robux pack worth $4.99 on Roblox, but the screen showed “payment declined.” I tried again, not realizing that the money had already been taken from my account. The same “payment declined” message appeared, and I still didn’t receive any Robux. I checked my bank statement and confirmed that two charges of $4.99 were made. This situation is confusing and unfair, especially since I received nothing in return. I would like to cancel the purchase from my second attempt and receive the Robux I paid for in my first attempt with the 500 Robux pack.