extra charges

I have been charged extra 10€ for the recent month. I am sure, I haven't made any international calls or haven't made any payments through my number. So could anyone help what is with that extra calls and service charge of. Normally my contract is of 27€ but now it is 37€ because of extra cost. I want proper showcase of where i have made mistake so that if I have really made a mistake i would not repeat it in future or if it is a mistake from your end then please get it fixed.

Edit o2_Kathi 09.12.25 Moved from the section o2 Mobilfunk to English o2 Community