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.

Can i activate a tmobile iphone 5c?

I found a iphone 5c without its SIM card in it and now i can't activate it. Can i jus buy any SIM card on amazon and activate it or does it have to be a valid SIM card that has service?

I didn't remove my sim card before trade in my iphone to at&t?

I trade in my old iphone 4 to at&t today and I forgot that my sim card is still in there! I erase all the contents and settings on the phone though. The guy there didn't say anything about it, but I change my phone number, so does this has anything to do with it? Can at&t do anything with it?

Please answer these questions! I'm worry about it so much right now!

IPhone contacts disappeared. How do I get it back?

All my contacts were on my phone yesterday. Today I noticed that all my contacts were gone, but in the recent calls, it was replaced by their phone numbers. My notes are also gone. I haven't synced my phone for a few days, and it hadn't crashed or anything, so is there a way I could get them back? I tried to sync it, hoping it was backed up, but that didn't help. It was weird how it just disappeared out of nowhere. I haven't tried to turn it off than back on, afraid that everything on my phone would be lost.

Added (1). This happened the day I was notified that I could update to iOS 7.0.3. Maybe that could be the reason my contacts disappeared?

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How can I safely take apart an iPhone? I know it will void the warranty. Are there precautions i have to take to ensure safety? Such as avoiding electric shock and such.