Greetings from iTunes Store Support. My name is Aaron, and I will be assisting you with your concern. I understand that your credit card does not work and when you tried to redeem the gift card that you have, you were prompted that it needs to be redeemed on UK Storefront. I know you must be surprised that you could not use the credit card and redeem the gift card. Don’t worry, I will definitely provide you necessary information that will lead us in resolving this case.
Muhanad, upon reviewing your concern, it appears that the given order MHBTN3N3F8 has not been paid. Unpaid orders will temporarily prevent you from purchasing. As soon as it’s paid, you can buy from the iTunes Store again.
This is the same reason why you could not use your credit card properly.
If the issue is that your credit card has been declined by your financial institution, contact them to find out why the card was rejected. If they're able to resolve the issue, you should be able to pay for the order using the same card and then continue purchasing with your account. If they can't resolve the issue, you can pay for this order with a different credit card or with store credit.
To review what the purchase was for and how to pay for the order, please see the steps in this article:
Pay an unpaid balance in the iTunes Store
https://support.apple.com/en-us/HT203005
You can also pay for this order by redeeming an iTunes Gift Card. Please see this page for more information:
Redeem and use iTunes Gift Cards and content codes
http://support.apple.com/en-us/HT201209
If you choose this option, after you redeem the code, the unpaid balance of the order will be deducted from your store credit balance.
However, iTunes Gifts and Gift Certificates must be used in the same country where they were purchased. The gift card you are trying to redeem is locked within UK territories that is why you were prompted to use it on the given storefront.
I hope this helps. If you're still having issues paying for the order, let me know. I'll be happy to help.
Sincerely, Aaron iTunes Store/Mac App Store Customer Support