What should i do when i751 takes more than 18months

[Y+B 1]

1 hour ago, mtldesai809 said:

did you received your 24 months extension letter?

No they didn't sent me the letter!!!😡
I called USCIS again on 10/1 as I was directed to do so to schedule an infopass appointment if I didn't receive the letter by the end of the month. When I called again on 10/1, I was told that they haven't sent the letter yet and they don't know when they will. 
Today, I finally got a stamp on my passport for 1 year extension so I don't need to worry about the letter anymore but I was quite upset that I could have gotten this stamp earlier and left the US if the person from USCIS (who told me about the letter to be sent by the end of the month) didn't he cancel my infopass appointment.

[Guido51 9]

hi folks, my i751 is pending at potamac for over 15 months and i have a pending n400.

 

on uscis website, "Estimated Time Until Case Decision" increased by 3 months. is this accurate? 

 

i would appreciate any help.