I bought an iTunes card now it is not showing up on iTunes account??

I bought an iTunes card about three days ago and redeemed it on my iPhone 5 when I purchased songs it charged my debit card instead of using some of the money off my iTunes card. I looked up my account on my iPhone and my PC and when I clicked on it... it erased my $15.00 credit from apple account. I tried re-redeeming my itunes card and it says its already redeemed but the $15.00 shows up no where on my account!! HELP!!! What do I need to do??