Extreme high mobile data traffic

Sony Xperia 10 III

I have big problems with mobile data traffic. I have a large data allowance every month. At the weekend, I was surprised to discover that this was completely used up. So I added 300 MB and after about 1/2 hour I was speechless that this volume had also been used up, even though I hadn’t used the smartphone. Yesterday it was same with another try.

I would now like to find out who is “stealing” my mobile data volume. Which program would be best for this? I first need to know the program/process of my smartphone and then, of course, the IP address of the other party

Sorry for that simple question but I don’t have any experience in network themes.

Nethogs from chum should work, just have to start it as root (devel-su nethogs) from terminal