I purchased a itunes card @ walmart and entered the code to redeem it then after multiple tries it still stated valid code.Apple wants my reciept but i cant find it.what should i do?

I purchased a itunes gift card at walmart and after trying several times it kept stating code was invalid . Apple states it needs the card and the receipt where it was purchased and I cant find my reciept. has anyone had a similar problem and if so or if you know in any way to help me please comment. I have already emailed apple yesterday and havent heard back from them yet so that is why i turned to other apple customers as yourself hoping someone could help me resolve this because i need that money on my iphone! thank you so much!