Public Mobile is not pay-as-you-go / pay-per-use, which would be putting money into your account, a then, when you make a call/text/use data, the price for that usage is taken from your balance.
Here it's pay-BEFORE-you-can-use-a-feature. If you don't have talk in your plan you can't call someone or receive calls, if you don't have texts as part of your plan you can't send or receive texts. If you don't buy an add-on for a service that goes beyond what is included in your plan, you cannot use it (if you have an add-on or metered feature and you run out of the amount you purchased the service will just stop).
On the flip side there are never any overage surprises.
