Call USCIS. Happened to me when I applied for OPT, I send wrong money amount and then never heard back from them. I called them after 40 days and they told me that I send the wrong MO amount. They have sent back my application packet to my apt but the PO office returned the packed back to USCIS saying my address is invalid. In my case, I send wrong MO amount so they never send me a receipt notice in my email or text.