Prepaid for 30 days, but after changing plans I had to pay again! What happened to the rest of the month I already paid for?

[Lincolncitylynne]

I don't get it.  If you already paid for 30 days, why can't you use them?

[Snn5]

Prepaid works differently than postpaid in this regard.  Money placed into prepaid accounts lasts 30 days, unless you bought the add-on data that lasts 90 days.  The add-on data does not begin until the base data is used.  Changing plans on prepaid should be done on the last day of the cycle.  No matter the amount there is a limit before expiration.