apps open on their own

Since the IOS 9 update, my apps do not close when I close them out, or they automatically open on their own. This is going to cause me overages on my cell phone bill each month because I do not constantly check my phone every 5 seconds and apps can run for several hours before I would notice. Other than completely shutting off cellular data for every single app, is there anything else I can do? Very disappointed in Apple after this last upgrade and been a faithful iPhone owner for about 6 years. I'm ready to switch to another product because of this.