Unusually high data usage
My iphone has unusually high data usage since June 2020. It is when I am asleep. It is using up to 2 GB of data a day! I close all my apps at night but it is still happening. It appears to be system services and wifi connect which I have now turned off. Any ideas on why this is happening? My cell provider says it is an Apple problem and not a service provider problem.
iPhone 6, iOS 12