How can I control the Data on my Phone

Month after month I keep getting this message from ATT:

"75% of your 3072 MB shared data has been used. If all 3072 MB is used before this billing period ends 12/14/16 we'll add 1GB of shared data to your plan for $15...." It is so frustrating. I have already added to my data amount and 3 GB should be plenty.... at least I think so.

So, I did some searching to find out what might be causing my problem. Some of these things did not help me, but I found them at different places than the website says, so I am going to list them here.  They are from http://macworld.co.uk/how-to/iphone

1. There is something in iPhone OS10 called Wi-Fi Assist which mobilizes the cellular network if your Wi-Fi is not working well. It is turned on by default, so it may be compensating when you don't want it to be. You can turn it off by going to SETTINGS>CELLULAR>Wi-Fi Assist and then turn it off. The article said that Wi-Fi Assist is under Mobile Data. but in my phone I found it under Cellular.
2. To see how much you are using and which programs are using the most go to SETTINGS>CELLULAR. As you scroll down you will see each of the programs on your phone and you can turn on or off the use of cellular with each one. You can also see how much each one uses by looking at the number underneath the app. At the bottom is a number that totals how much you have used over time. You can and should clear this every month so that you can see what is changing.
3. You can download an app that manages your data usage. I decided to try this and went to the app store. I searched for Data Management and found a free app that I am trying. It is called My Data Manager.
4. It is important to realize that all of your apps that are allowed to use Cellular Data are checking for updates and updating in the background when you may have no idea that the Cellular Data is being used.
5. You can totally disable the use of Cellular Data and if it is near the end of the month and your data is running out you may want to do that temporarily so that you don't run over! This will turn off email, web browsing and notifications.
6. You can change your settings in Facebook so that video does not automatically stream unless you are in wi-fi. 
7. Stop iCloud Drive from using cellular data. Go to SETTINGS>iCLOUD>iCLOUD Drive and turn off Use
   
   Cellular Data. 
8. Check under SETTINGS>iTUNES AND APP Stores to make sure that Use Cellular Data is turned off.
9. Make sure that you have turned off Data Roaming. This will not make any difference in the US, but will not allow you to make calls in other countries.

Basically, I learned to be more conscious of when I am using Wi-Fi and when I am using Cellular data. Wi-Fi is a service that you contract for at home and many businesses and coffee shops contract and provide for you. You almost always have to put in a password to access Wi-Fi. Cellular Data is what come from the Cell Phone towers and YOU are paying for it when you pay your cell phone bill. That is why your bill can get crazy!  

So, I am going to do my best to use the Cell Phone Towers for phone calls and occasionally for driving directions and do as much as I can with Wi-Fi.

REMEMBER:  Public Wi-Fi is not a secure place to do anything private. If you are shopping or doing banking be sure to use your own protected home Wi-Fi.