O2

Yes, you are right. I just found out that it was the daily charge for data (even tho I wasnt use my phone). So tricky.

Thanks for your reply. No, my SIM wasnt even activated before. I just topped up with £15 for the first time, and when I went back to the O2 app (after 20 mins) to check if its active yet or not, I noticed my balance is only £13. I will probably call ...