Q: iPhone 6 using data/ wifi in background by itself

Hey Abhijeet,

You can find out what applications are using your cellular data as well as turn off usage for any applications that are using excessive data by going to Settings > Cellular > USE CELLULAR DATA FOR:

See this article -

Learn about cellular data settings and usage on your iPhone and iPad (Cellular Model) - Apple Support

Thanks for using Apple Support Communities.

Be well,

Brett L 

Hi Abhijeet,

Thank you for using Apple Support Communities. Due to the nature of the issue you described you may find more information by using another one of Apple's support resources - https://getsupport.apple.com/GetproductgroupList.action.

Brett L