iPhone makes small data roaming traffic despite DISABLED data roaming and disabled mobile data

This is about my wife's iPhone 11 and involuntary data usage.

My wife is currently abroad, and has both data roaming as well as mobile data in general deactivated. Nonetheless, for the last few weeks her iPhone has apparently made (very small) roaming data connections, mostly 1 or 2 KB, but sometimes up to 16 KB. Sometimes several times a day, sometimes not for a few days. Every single time this happens, a fixed amount is charged.

This should not happen! I have already inquired with our mobile provider, and they maintain that these data connections were made, and are probably the iPhone itself checking for updates or whatever.

Anyways, this is very concerning. I found a similar post from half a year ago (My iPhone X makes small roaming data traf… - Apple Community), which was closed without any proper resolution, and am hoping you guys can help us more!

Thanks in advance!

Cheers,

Pascal

PS.: I'm absolutely sure all data is deactivated, I did it myself when we were on the plane before taking off, and I asked her to check again now that the bill came in – it's still deactivated.