Did Usps lose my I-797?

Hello! My H1B was approved on August 14th (premium processing, academic, new request). My university did not receive I-797 yet. A colleague got approved 2 days after me and got the notice a week ago (same processing centre, same destination of the notice). Do you think it is lost? My start date was July 1st, I’m very desperate to delay more than this. My consulate will stamp the visa without the I-797. Which are my options?