Hello, I filed form 843 along with the required documentation in April to receive FICA taxes refunded, as I was on F-1 status. I received a letter end of May saying a document was missing. Sent everything back and I haven't heard from the IRS since. I called the IRS advocate number and the lady told me she coulnd't see anything in the system and that maybe they did not receive my documents. I don't think this is possible. (She even added that after I received the letter in May, my case was closed and that is why nothing showed in the system - absurd)

Also, I might move to a different state in a month or 2. I will change my address through USPS but I believe my mail is only "guaranteed" to be delivered to the new address for 12 months.
What should I do?

Thank you!

Form 843 processing can take up to a year.

Once you move, call the IRS back to check on the status of your submission. If they say again that there is nothing on the system, then re-submit.