Owe money on account (unaware until i couldn't do anything about it)

So i bought three songs on itunes, i was unaware of the amount of money i still had left. Itunes never told me i ran out of money or didnt have enough left. So now i cant do anything on my accout. I can't even update a free app. now that i know i would refund those songs and get my money back and get the songs some other time.