The first thing to do is to contact your attorney and share the information about this USCIS officer's call. If the employer has not been notified first, then it most probably is a scam call. You should send your H1B documents to someone who can be legitimately verified. Ask them to send you an email from their official USCIS email address. The official email address should look like FIRST-NAME.LAST-NAME@uscis.dhs.gov Do not email your documents if you cannot verify the USCIS email address.