I have a $61.40 prepaid balance. My phone shows "payment due" in 7 days. I will never use up my balance in seven days. Why is there a payment due if I will have a $61.40 balance?

[G_Y]

I have a $61.40 prepaid balance.  My phone shows "payment due" in 7 days.  I will never use up my balance in seven days.  Why is there a payment due if I will have a $61.40 balance?

[Snn5]

This is an automated message.  I am on auto-pay and have had a credit in the account as well and the payment is just auto-paid or uses the credit in the account to make the payment.