My itunes credit is gone

Is it possible that you'd spent it, and that what you were seeing was an out-of-date balance (I've sometimes seen out-of-date balances on my devices/computer) ? Logging out and back into your account should have no impact on your balance (apart from it possibly updating) - you've checked your account's purchase history : See your purchase history in the iTunes Store on a Mac or PC - Apple Support ?

If you believe that you should still have a balance (and have tried logging out and back in again) : emea

You've tried logging out and back in again, and checked your account's purchase history e.g. no subscriptions or pre-orders were due ?

As well as showing at the top right of the store's pages, my balance also show under my id when clicking on my name towards the top right, and when logging into my account (Store > View Account, between Country/Region and number of computers authorised) - you're not seeing it in any of those places ? You could try contacting iTunes Support via the link in my above reply (https://www.apple.com/emea/support/itunes/contact.html)

Same thing happened to me! I dont know where the $ couldve went. I had a $50 iTunes gift card and I bought a $20 album. Weeks later it now says $0.07 balance and I haven't purchased anything else. on my purchase history it only says that 1 album I bought.

Did you iTunes anything when you redeemed the card ? If you can't see where it went contact iTunes Support, use the above link