Data usage control - use wifi

You're right. When WiFi is mentioned, they mean external WiFi or wired home internet. If you're using a hotspot device there is no way to lower data usage except for literally using less data. I would recommend not using any Windows PCs if you want less usage. Windows doesn't discriminate, it can't tell if a connection is mobile data or not. So it will do updates, it will use as much bandwidth as a connection gives it. A web page on IE or Firefox or whatnot will use 3x as much data as the mobile version on a tablet or phone.

Sorry,   my daughter's I-phone is using up all her data, even connected to our home wi-fi and when she is in coffee shops.  This is getting disgusting.  

My kids all have their wi-fi assist turned off, and A T & T is still saying our usage is higher....what is up with that?

Do your kids stream music from online sources (Spotify, Apple Music, Pandora, etc.)?  If they do this, and their phone screen goes dark, they are likely using cellular data to stream most of that music and not using wifi.  Many of the cell phone makers have setup their phones to turn off wifi when the [hone's screen goes dark as a way to claim they have longer battery life.  In the end that means that their phones wil often use cellular data even though they have wifi readily accessible.  The solution to this is for them to either prevent their screens from sleeping, or in many cases, to connect their phone to an external power source, so many of the cell phone OSes are also written to not turn off the wifi if on external power.  This has been a known issue with Apple iPhones since at least as far back as the iPhone 3G (about 8 years ago).

The only accurate information on data use is on the phone itself.  Look in settings under cellular data usage.  Scroll down to see which app is using large amounts of data.    With young adults it is typically social media or streaming media.   

Once you have a better idea what, put the responsibility on the user.  Your child is responsible for reducing these numbers or paying for the extra data.

Anyone can do a quick data check by dialing *3282# anytime, a text will show data by number.

You also have the option of turning off a users data in the My ATT app.  Sign in manage the devices and turn a users data off.  It will automatically turn on at the start of a new bill cycle.

Watch out for AT&T.  My old AT&T modem was destroyed by a power surge. I had purchased it. AT&T rep put in a new modem.  I must pay $10+ (with added taxes) per month to lease the new AT&T modem.  I am not allowed to buy it and there is no compatible modem at Best Buy or Fry's to buy.  Once they get you, you are stuck paying the lease payment.  Pretty crummy, right?  RC

@Beavis28.  All electronics should be plugged into a surge protector.  Power surges can destroy a 100 router or a $1000 flat screen TV set.  

Please go over to the Internet forum to ask about your router options.  You are not required to spend $10 each month to rent a router.  But if you chose to own a router, you have to replace it at your own expense.  

I know about surge protectors - I now have them.  Can't buy another AT&T compatable modem and AT&T quit selling them.  Now I have to pay to lease a modem - very bad business.