Last time something like this happened to me it was FedEx and they lost the package. Called Summit on the 3rd day it didn't show movement. Rep was like "yep that looks lost" and the next day they had what I ordered on my doorstep overnighted. I'd be calling UPS or the store you bought the part from if you see no movement tomorrow.
2000 Mustang GT Steeda build #48. Bolt ons, suspension, Novi 2000.
Just because I give you advice, doesn't mean I know more than you. Its just means I've done more stupid ****.