I just purchased a 500 minute talk booster add on. My current 100 minute talk booster has about 10 minutes left. when I checked my account information/transaction history it shows a $25 credit but doesn't clearly state that there is a 500 minute booster "on deck". I want to ensure that I do not run out of minutes. How can I ensure that the 500 minute talk booster add on is going to "kick in" when the 100 minute booster runs out?