I ran out of money on my prepaid visa giftcard, but payments still keep going through?

Okay so I got this prepaid visa gift card that I've been using online lately, on my Xbox, and also on my iPhone. But payments still keep going through and when I go online to check the balance it's at.41, but I can still buy things. I'm hesitant to keep buying things seeing as my uncle bought it and I don't know where they are taking the money from. Thoughts?

My guess is the company your purchasing from only charges the card once a day. Once apple and xbox notice the problem your accounts will be locked until you provide a new form of payment and pay for your purchases.