My green card application never be picked up from Chicago PO box more than 2 weeks

[fon3m]

Hi,

I submit my green card application by USPS. It arrived at PO CHICAGO on February 4, 2019 at 5:55 am and show In-Transit status until now. It been there for 18 days. I called USPS Chicago but no one pick up. What should I do?

Thanks!