It looks like you didn't read the description or didn't know what you were doing. The name of the website you bought it from is called EveryGunPart.com. They sell gun part kits, not complete guns. Also, you can't buy a firearm on the internet and have it mailed to your house, that's a felony. You can have gun parts sent to your house but the not the serialized receiver. I think you just didn't know what you were doing.
I'll add that you can't buy a receiver for this gun. It's not something that exists anywhere You just have to go buy the whole gun from a gun store.