Playing phone tag with the USCIS is always a fun way to pass time.
I've played it a few times. They will actually call back. It is usually within a few days and they will give you a pin/confirmation number to prove it is them and not some scam.
After an infopass appointment is made, tier one needs to send you a confirmation document by email with the appointment info. Print it and bring it with you to the field office.
If you haven not received the email within a day, call back and try to get confirmation that the appointment is actually made, you may have to insist to be escalated to a tier two officer. They cannot resend the mail but can send you a different email with a confirmation number on it. print that one and bring it.
You will not be let in to the office if your name is not on the list at security and most of the time they want to see some paperwork from you confirming the appointment.