Apologies in advance for the likely TL;DR.
I have an iPhone 5 running iOS7 on a PAYG deal with Vodafone in the UK. Whenever I top up £10, I get a 500mb data pack that's valid for 30 days. Thing is, I don't need to top up very often (as an example: I last topped up on March 4th, and I still have £6 of credit left), so my mobile data pack will frequently expire before I need to top up.
As of February this year, I started getting messages from Vodafone at random times saying "We noticed you've started using mobile data, so we've charged you £1 for 25mb of data". The problem is that every single time I've had this message, it's after I've come back home and been using WiFi for a good long while.
The first time I complained about this, the rep I spoke to said "Oh, the system miscalculates it all the time, I'll refund your money. You can always turn off mobile data and it won't happen again."
I duly did this, and the second time it happened I complained again, and the rep I spoke to said "It doesn't matter if you turn mobile data off; your phone uses it anyway in secret to do updates."
This has happened three times subsequently, and twice I've been told the same thing: even if I have mobile data turned off, my phone will turn it back on all by itself to check for updates, then turn it back off - and it's that microscopic data use that I'm getting charged for.
This sounds like utter horseradish to me, but is there any truth to this? I've gotten into the habit of turning off Mobile Data and Use 3G when I'm out unless I need to use it; in addition Data Roaming is always off, Background App Refresh is off, and Limit Ad Tracking is on. Am I missing something?