My Order Is Late. No Response!

I placed my order with Walmart online on May 1, 2013. One item from my order arrived on time, no problem at all! But the other part of my order is late. It was supposed to arrive this Tuesday (May 7th), but every time I check the delivery status it says "processing". When I tried to submit an inquiry on their web (and I did it twice), I haven't got a reply back, as if nobody cares. I wanted to get my order on time, that's why I agreed to purchase from them in the first place. If I knew how irresponsible their service was, I'd have never placed my order in the first place. They haven't even shipped it yet, not alone "delivered". What can I do to fix this problem? Would appreciate your advice/help! Thank you.