Can I buy a prepaid card with a Media Markt voucher at Media Markt?

I tried to buy XBOX credit (30 euro) in the Media Markt online shop with a 30 euro voucher card that I got for Christmas. Unfortunately, I'm only offered credit card payment for such cards. Why is that so?

Could I try to buy a card in the store with my gift card?

The purchase of vouchers with vouchers is not possible at MediaMarkt & Co. It doesn't look any different in the store.