Please accept my heart felt condolences for the untimely death of your son. I think you need to engage an immigration attorney at this point and file an action in Federal court of competent jurisdiction asking that the Federal judge adjudicate your naturalization application. You have the right to do that and you should use this right.
The information contained in this answer is provided for informational purposes only, and should not be construed as legal advice on any subject matter,not should it be viewed as establishing an attorney client relationship of any kind.
Heart felt condolences for the untimely passing of your son..
By law, USCIS has no more than 120 days after the interview to issue a decision on the case. You are well beyond that period and from your recounting of it have already exhausted all your "administrative remedies" (went in the USCIS Office 5 times with 5 infopass"). You are now entitled to file a Mandamus Action in Federal Court, demanding that USCIS finally fulfill its obligation to timely adjudicate your case. You will prevail. As soon as your immigration attorney will file the suit, the local "assistant district counsel" from the US attorney's office which will be assigned to defend USCIS in federal court will literally beg your attorney to drop the suit (and will act as your best advocate with USCIS to pressure them to approve your N-400 without any further unnecessary delay!) (Forget about any Congressperson, that never yields anything... All they do is "talk, talk, ...but achieve nothing..)
Kindly be advised that the answer above is only general in nature cannot be construed as legal advice, given that not enough facts are known. It is your responsibility to retain a lawyer to analyze the facts specific to your particular situation in order to give you specific advice. Specific answers will require cognizance of all pertinent facts about your case. Any answers offered on Avvo are of a general nature only, and are not meant to create an attorney-client relationship.
You have to call the USCIS hotline at 800 375 5283 and once the officer brings up the case on his/her screen you would have to ask for "a case service request". The Infopass is limited to only a specific processing center and it would not get you anywhere. Once they do the service request you will have to write that number down and in about 10 days you will receive a letter in the mail giving you a time frame and what is the status of your case.
If you do not get your result within that new period you can then file a Writ of Mandamus attaching the call request. An info pass is not enough to show what is going on. Most likely your case is still pending because your criminal background check has expired and it may take a lot for your country to send their update, or they just forgot to send you a new appointment to be re-fingerprinted.
Regardless of the situation if you do not obtain a response within the time frame presented in the new letter (service request) you should hire an attorney as the Writ of Mandamus is not something you can do on your own, it is in Federal Court and procedures are pretty strict even with pro-se (people without attorneys)
I wish you best of Luck.
Should you wish, I offer one hour free initial consultation.