Until case is past processing there is nothing that can be done. Our I-751 was filed in May 2019 and we been waiting for Interview since Sept 2019. We filed N-400 in May 2020. We inquired our case and USCIS responded that we will have a combo interview. Our Senator said that they will only inquire if our case is past processing. In June 29th 2022 our case was past processing (USCIS extended normal processing twice from the 3 year from receipt date). I inquired with USCIS and my Senator in June 29th. My Senator responded on July 15th asking I submit two separate request for N400 and I-751 (I had combined them in the inquiry I sent previously). In July 19th Senator sent inquiry to USCIS on my behalf.
Around Mid August 2022, I received a response from USCIS about my inquiry which was basically the same response I received two different times that is I will have a combo interview.
In August 22, 2022, my Senator shared USCIS response which mentioned that I will have a combo interview and I am in line for an interview. They requested respectfully to be contacted within 60 days if my interview is not scheduled by then. This looked promising and very nice response to my Senator vs the response I received. For the first time I had an update in my case when I viewed the status: I-751 status was that my case was being worked on actively and date updated was from Sept 2019 to Aug 22, 2022.
In September 13th 2022 my status now is that an interview has been scheduled and they will mail the interview notice. Now we can't wait for the mail to be sent.
I think patience is key and just continue living your life eventually you will get your interview scheduled. The issue with pandemic and politics is hopefully behind and process becomes better. USCIS is moving to risk based approach for I-751 and hopefully this will free up immigration staff time and clear the backlog.