Q: i need to know how to find out how much money is left on an itunes gift card

Once a card has been redeemed then its amount should be on your account, the card itself is now effectively zero. My account's balance shows at the top left of the store's page on my computer's iTunes, and by logging in to view my account via the Store > View Account menu option. On my devices it shows at the bottom of, for example, the Featured tab in the App Store app under my account id (or you can view your account via Settings > iTunes & App Stores and it should show on the screen that you are taken to)

I don't understand..

Which bit don't you understand ? When you redeem an iTunes card onto your account the card's value gets added to your account - the actual card is now used and empty.

To see what balance that you have left on your account (if you still have a balance) : See your iTunes credit balance - Apple Support

I'm trying to deactivate my two purchased itunes gift cards because I bought them to pay a "supposed" fine. Which turned out to be a scam. And all I'm trying to do is get my $200 back. Please Help.

What do you mean by 'deactivate', what exactly are you trying to do ? And what 'fine' - iTunes doesn't apply 'fines'