First off I will mention that someone needs to home because the SIM needs to be signed for. If you were not home a door tag should have been left by FedEx for you to sign and it would be delivered the day. If you know for sure it was lost by FedEx or returned to Visible you will likely need contact customer service so they know and they should be able to send you another or explain how to go about getting another one. To contact them use chat on your account page, little blue box bottom right corner, type live agent so you are not talking to a robot. You can also contact them via Twitter or Facebook messenger, both icons/links can be found in the bottom righthand corner of this page.
