Lost money

I had 6 dollar and something cent on my account and I redeem 50 dollar gift card. I bought 500 marketplace cash in Dc Universe for 5 dollar and 37 cent and I did not buy anything else. I had 51 dolar left and some cent. After a week I check my balance
I only had 34 dollar and 86 cent. Where did my rest of the money went no one else use my xbox expect for my self and I did not buy anything. Please do something about it and I even check my order history my letest order history was buying 500 marketplace cash
in dc universe for 5 dollar and 37 cent.

:)