I-751 and N-400 question?

I filed N-400 while my I-751 was pending for a year. I passed N-400 interview and test and have I-751 approved at the same interview. However, I haven't been scheduled for oath for a long time though a lot of people interviewed N-400 after me already took the oath.

I spoke with three officers at Infopass and each time get something different/new.

The first officer told me that everything got final approved and my name check and biometrics are cleared and valid. She asked me to wait for oath letter.

A week later, the second officer told me that my I-751 is pending, there is no way I can proceed my naturalization. she told me that my I-751 is at California Service Center (it was originally sent to NSC) and on the system it says that there will be an interview, but she is not sure if it is for I-751 or N-400.

The third officer told me that USCIS need another officer to reverify my I-751 interview and it takes time. She asked me to wait.

Does anyone have similar experience? How long does it take to clear my I-751 and have my oath scheduled?