AT&T overcharging me over iPhone data?

So my family and I recently just upgraded our phones (before I had a smartphone) to iPhones, my whole entire family has iPhones. We've been with AT&T for about 3 years now and we always seem to have problems with them, and don't say to change networks because my Dad won't. But all I really do on my iPhone is go on safari (and we all share the same data, the family plan which consists of 6144 MB, and we have unlimited text/call. Instagram, play games, apps (all my apps are free) and I never buy anything on the app store that costs money. Normally the phone bill would cost around 200 a month, but when we got our phone bill this time, it was TWICE AS MUCH. $400 something. My parents are freaking out, and we're going to the AT&T store tomorrow but I just want to know if it's a mistake so I don't have to freak out as much. I'm wondering maybe it says the app is free but when I use it, it costs money without me knowing of it. And the apps I have are- Find iPhone, Snapchat, Picsart, Instasize, Instagram, Split Pic( i never rlly use this), CamWowPro, GameUrVideo, PicLab, MagicHour, Keycam, Shazam, Temple Run, Sky Burger, Subway Surf, Egg Baby and HS Story. I never buy anything on those apps either. (like coins and stuff) Please help if you know anything about this.

They LOVE people like you…

1. When you buy apps, it has to be through an already set up credit card… It will not ever go to your phone bill.

2. If you recently upgraded, you are going to be charged a TON of activation fees and various upgrade fees. When my family upgraded this summer, it was the exact same thing. The bill was about double. This is because they charge a month ahead for data and so you were charged for next month as well as this month. They also charged you upgrade fees and activation fees for all lines. As your parents will find out tomorrow, there's nothing that ATT is going to say except tough luck.

3. If your entire family is sharing 6 gigs of data, then it is easily possible that they have gone over their amount… I use 3 gigs a month myself.

4. No apps will ever charge you money if they were free unless they ask for a credit card and you give it to them. Like I said above, apps and things that you buy on the app store DO NOT get charged to your monthly phone bill.

Hope this helped!