Q: Got an iTunes card with no barcode- where can i find the serial number?

It's neither of those (it is an iTunes card, not an Apple Store gift card ?), you should have a peelable strip at the top back of the card which reveals the redemption code (and which should start with an X) : Redeem iTunes Gift Cards and codes - Apple Support

The last one that I bought looked like (not sure if they've changed) :

The great strip at the top is removed to reveal the code.

The codes that you gave are what the shop have used to activate the card (probably by scanning the magnetic strip), and possibly show on the receipt - the code to redeem the card onto your account is under the peelable strip

Gift cards don't have a barcode, they have a character redemption code that starts with an X.

The GCA number is presumably the gift card number, not sure what the numbers on the bottom is called, presumably it's for Apple's use to potentially help get the redemption code if the person scratches it off.

You could try contacting iTunes Support and see if they can redeem or give you the redemption code (you will probably need to give them images of the front and back of the card, and its receipt) : http://www.apple.com/support/itunes/contact/

According to If you can't redeem your iTunes Store Gift Card or code - Apple Support

The GCA is the serial #