Question about the balance and the expiration date
Since I am going to leave for my hometown, I changed my plan to a pay-per-use plan. I firstly refilled my balance with $50 and found that the expiration date is Aug 30. Then I refilled $50 again, finding the expiration date did not change. But my friend refilled with $100 at once and his expiration date is Jun 1, 2021. So why my expiration date did not change after I increase my balance, how can I extend my expiration date.