The Google Chat setting, along with many other settings that haven't migrated over to the new user interface, is on the "Legacy" version of the user interface (the old web page). If you're on the new user interface, click the three-bar, "hamburger" icon in the upper left corner of the web page, then scroll down to the bottom of the left side, and click the Legacy link.
However, that's not your problem. It's more likely that there is some other issue, given that the other two OBi's work fine.
Typically, when you can make outbound calls, but not receive inbound calls, your OBi is either authorized to the wrong Google account(s), or the authorization got deleted somehow. You said you deleted the accounts and set it up again, but it didn't work.
I suggest taking the OBi home with you, and plugging it into the same LAN as your working OBi. Make a call to one of the GV numbers from some other telephone number, not one of your Google Voice numbers, and not from your forwarding cell phone number(s).
The phones attached to both OBi's should ring. Do that test and report back.