Hi,
I've had the same problem. I've got an iPhone SE 2nd Gen & downloaded IOS 16.2 on 19th December. Then on 21st Dec I got a message from O2 (my UK mobile network provider) to say I'd almost used all my 10GB allowance (I usually use about 2GB a month) When I checked my Mobile Data use it was "System Services/General" (SS/G) that had used 9.4GB.
O2 gave me another 2GB but my phone used 1.4GB in 30 minutes all under SS/G so I had to turn mobile data off which is a pain TBH.
Note that I've tried turning off Wi-Fi assist, Background App Refresh etc & it's made no difference. However, prior to installing ios 16.2 I had these on & didn't use all this data. I've also reset network settings, logged out of my Apple ID & re-installed the operating system none of which have made a difference.
I've been onto Apple Support over the Christmas period & they are looking into the issue but I want to know how many others are having the same problem as Apple say mine is an isolated case & if they've managed to resolve it?
Thanks in advance