Thanks for everyone's recommendations on what to do! I tried sending in an inquiry about a "lost approval letter" and I got this response back "Your case is under active review by an immigration officer. You should be receiving a decision or notice of further action at the address of record shortly. If you have not received a decision or notice of further action within 120-days of this response, please feel free to submit a new inquiry by calling the USCIS Contact Center." I really don't want to wait ANOTHER 120 days since I have already waited 120 days since my N-400 and I-751 combo interview. I have now submitted all my information to my local US Representative to see if they can help speed up the process.