Gift card issue

My friend Paul bright three gift cards two weeks ago, he never buy gift cards before, so he didn't know if he want to unlock the credit in gift card he has to pay for it, but he put one gift card in paying machine( i don't know what's that called) twice, which means he paid same gift card twice, so this the credit in this gift card is not unlocked, i went back to walmark but the people work there said i have to call you guys, but i can't find the contact number, and since I'm lazy (lol), so i didn't call at all. The reason why I'm here is that i hope you guys can help me to unlock the credit in this gift card pls, thank you so much