Roblox complaint: Robux

My son bought a roblox card with some of his birthday money. When he went to redeem the card, it wouldn’t work. We reached out to roblox support and told them and then sent photos of our card and the receipts as requested. Our issue was then sent to the billing department. After a few days, the billing department told us that the store that our card was purchased from had not activated the card. I then went to the store and they ed that the card in fact had been activated and I also have a receipt where this is clear. I then sent another message to roblox billing department and told them. They told me basically that they couldn’t help me. I am beyond upset! This is ridiculous. Roblox customer service is unhelpful and unprofessional. My child spent his birthday money on a roblox gift card and even with proof and the receipt, he is now out the money. The store where it was purchased from does not refund for gift cards. Roblox did absolutely nothing to help! Are these cards a scam?