How do you report a problem dealing with something being on your card you didn't buy?

I went to check my emails and it said that I had been charged 5 dollars and some change... after doing my history research one of my friends had downloaded a game and bought something with-in the game. Now Im wondering how do I fix this? I dont want to pay because it was a mistake and I didnt buy it, also I do not want to ask them for money for a mistake. I want to know is there any way I can remove it, does the company have a online chat or something where I can talk to someone about this? This is really bothering me because I really dont want to pay, I need all the money I can get. Someone please help!!!!