I do have iCloud backup set - but I always have had it and NEVER had this issue before! The vast majority of time I am connected to WiFi...yet this month I have now rattled through about 10GB of data!!!
my phone is even saying that a small amount in last few days was used on FaceTime...however I haven’t used FaceTime (only on my iPad which can only connect to WiFi anyway!). Haven’t touched FaceTime on my phone at all.
I have just nipped out for 20 mins and come home to find data totally gone. More has been added - I don’t know if this is from the person I was talking to from virgin who is so called monitoring my account?...or if this is something I’m going to find myself charged with at the next billing period (I seriously hope not!!!)
Can you show us a screenshot of the app usage page and can you check your online bill to see the itemised internet usage? It doesn't show you which apps but will tell you the rough times when data was used. This is useful when you're trying to pin point what may be used. You can try uninstalling apps and slowly adding each one to see which one may be the culprit.
Please make sure that you're actually connected to the WiFi network when using certain apps as you may have accidentally been kicked off the network and use data instead.
If you set your billing cycle to 19th (yesterday). It will show you what your phone thinks has been using your mobile data in the last 24 hours, You can also set it to Tuesday and see what that says for the last few days