I got a huge bill when I switched to this plan, seems like they just added unlimited internet to all the lines. I told them to start it in my next bill cycle that started on the 7th of this month. WTH!?
About 2 pages back I spoke about this. What they do is they refund your previous months bill, then charge you for last months bill at the new rate and the following months.
The refunded bill should make a credit. If not, take a look and make sure that when the charged you for data and text at the new rate for the previous month. If not, call customer service and get a credit.