Mobile data not working on Android

Sometime earlier this month, mobile data just stopped working on our Android devices.  We have four phones on the plan, the iPhone still works, but all three Android phones can no longer connect to the internet unless we are connected to WiFi.

Talked to a rep last night that had me reset network settings, but all that did was forget all WiFi passwords.  Toggling airplane mode and rebooting have also been tried many times, but no success.

What can be done to get data working on our Android phones again?