Do you mean that you can't open apps or that the internet connection doesn't work? Do they work on Wi-Fi?
If you're saying that data is working, please log into your Self Serve account. If nothing is mentioned about hte amount of data used under Data & Add-ons, that means that all data has already been used.
If you mean that one speicfic app won't run, try force stopping, clearing the storage used by the app, uninstalling it, and then reinstalling it. Please be aware hat this will erase any preferences/settings and user information saved within in them.
Are you getting the circle of death? Try @computergeek541 suggestions. If they don't work check to see if your web driver is disabled. If so open the app to turn it back on. You may have to install any updates available first before it will allow you to open the app and enable the web driver.
Is that any particular app which refuses to load or ALL apps are misbehaving?
Usually if app is incompatible or signature is different it will not install at all.
Can you uninstall it and try to install it back?
Worst case scenario would be to reset phone to factory default and start from scratch. Backup everything first!
For few important apps I use almost daily, when update is offered I first do a backup of current version and then apply an update. And NEVER allow apps auto-update.