So you're not sure if you did receive it and it was thrown out? If you are sure you absolutely did not receive it. You should file a claim w USPS. Maybe they can help you figure out what happened. I'm not 100% sure but if its USPS fault they should help with a letter stating it was lost you then might be able to use this for replacement with USCIS without paying the fees again. I've overheard immigration attorney about this. Good luck!