Missing balance on my iTunes account!

I am getting very frustrated! I had bought a book about 4-5 days ago from my balance on my iTunes account, leaving me with a balance of around $7.32 ish, I wanted to buy another book but didn't have quite enough, so I put in another iTunes gift card of $25, which should have left me $32.32 now on my account. Though after putting my new $25 card in, the rest of my balance is no longer there! I am very frustrated since the apple people are telling me to check my history, that I have already used it. When I go into my history there is no purchases or any history in there and I know I did not use it up in 4 days!! Why is it always a fight with apple to get them to listen to you?