Please help?

I was on my game and i wanted to buy something for it so i put my debit card information on it and bought the stuff for it. I also allowed my bestfriend to use the same information to get some of the stuff for his game as well. After i bought the stuff and checked my debit card and it said that there was still 2$ left on the card i decided to stop buying what i wanted on the game. Since I bought the stuff I can't Download any free apps or update any already downloaded apps on my iPhone 4s. Every time I try It says, "There is a billing problem with the previous purchase." I need help, I don't know what to do, Please help?