I would make sure nothing is muting notifications by checking notification settings first. To check data usage, navigate to settings > wireless & networks > data usage. You can also try turning off your phone for 30 seconds then back on. If this fixes it, you can click accept as solution for this post.
Is that a phone setting?
Try one or more of the below:
*turn off your phone, leave off for a minutes, then reboot
*removing your SIM for a few minutes, then reinserting it
*go into airplane mode for a few minutes, then going back to regular mode
Plans here are 30 days, not monthly. So renewal will fluctuate.
If you are an Android user try downloading the Data Witness app: https://play.google.com/store/apps/details?id=com.iwik.datawitnesspm&hl=en_CA&gl=US
I use it, and it works great.
If you are Apple, I am sure there is an app that can track data by 30 day cycles as well.