I recently recived some necrons from hillycity-comics.com with a few blister packs in the order. As I was opening the little double blister boxes, I noticed one of the Immortal blisters had a Flayed One body, instead of a Immortal body, in it. Now I'm not sure what to do... Should I contact hill city, and ask for a new blister, or drive down to my local gw store and explane what happened to them, and hope they give me a new peice. Thanks for your help.

you'll need to contact the supplier

Contact the ones you got it from, it's their chore to send back flawed blisters to GW.
It will be better if you haven't opened the blister. Most likely you will get a new blister when you send it back, also ask for some cash that you used to ship the mini to them, 'cause it's their fault after all.