f it's a debit card that might be why it's being declined. It is clear in the entry form it says credit card/ debit card. Also last month I was in turkey store and was able to pay icloud storage with the same debit card. So this should not be the issue.
For a card to have a chance of being accepted it needs to be registered to the same name and address (including format and spacing etc.) that you have on your iTunes account, and have been issued by a bank in the country where you are (and therefore the country which is on your iTunes account). As I said it is %100 same.
If you are currently living in the UAE that is the country whose store you should use. This is not mandatory, I did it before so I don't think this is the reason.