Can't make or receive calls, due to account thinking that I don't have enough balance.

For the past week, I've been having a major issue with my cell phone.  Every time I try to make a call, a recording comes on, informing that my current balance is not enough to make the call in question.  But that's not true, as I know for a fact that I currently have $30 in the balance.  In fact, when I call my #12-3, I am informed that yes, the $30 is there.  So why does it think there isn't enough to make a call?

Calling Customer Service is hopeless, as the AI bots won't let me talk to a human.  Please help me!