I using an iPhone 6 plus on iOS 9.2. I was advised by my network provider that even if "Data Roaming" is turned off and even if "Mobile Data" is turned off, apps might still be consuming data in the background and the only way to prevent any data from being consumed is to disabled it at network level. By disabling "Data Roaming" and "Mobile Data" at phone level, it wouldn't do the trick. I was advised that this applies to every network provider throughout the world. Wonder if there's any truth to that. Anybody experienced the same issue of doing all the steps at phone level and still ended up incurring roaming charges.