h1 approval document went back to uscis because post office couldnot deliver it

[R5859]

hi all,
my approval document went back to uscis due to address issue i have raised a service request to send the document again its been more than a month but still no response. i am approaching 240 days dead line. in that case what should we do? we tried calling uscis they were saying since we are not petitioners my employer need to call them and ask for progress.
since i am approaching 240 days and my extension got approved can i work after 240 days?