I have Straight Talk and never go over the data.
The KEY is to 'shut your data off" when you are not using it. The only time my data is on is when I am looking something up and then it gets shut off.
Also,The more apps you have on your phone the more data is being used by the apps. The apps use about 1/3 of your data, running in the background ALL the time whether you are using them or not.
When you downloaded the app You clicked ok without reading the privacy policy? You gave them the rights to use your data when ever they feel like it. some even state they can turn your phone on to use data. And they DO!
Why do you think so many are for free? :W They use your data and then the consumer usually upgrades their plan to get more data from the provider. Revolving $doors$ between providers and app owners.
Your battery will last longer also with no apps.
New phone no apps my battery will last over a week.
Phone with apps, and data left on, I'm lucky to get thru the day.