My I 485 application was approved on 17th of march 2009.I got approval notice on 23rd march on 1st of april I got email that my green card back to them as un delivered (copy is attached)
"On March 31, 2009, the post office returned your Card as undeliverable. We will hold it for 180 days from March 31, 2009 to allow you time to contact us. If you do not contact us at 1-800-375-5283 within 180 days, this document will be destroyed and you will need to file a new application or application for replacement with fee."

I already call them they said I will get response in 45 days
I want to know am I suppose to file I 90/or just wait for uscis response