All of my EK tickets originate in HYD. That being said, up until a few months ago, they only accepted MasterCard and visa. The first time like a few years ago, I tried my 2 masters and my one visa, which were declined. I usually had to call MasterCard, and had to stay on the phone with them while booking it. Visa never worked, not sure why, but MasterCard ended up working after 2 attempts, a call to EK and a call to MasterCard. I prefer using my Amex cards so it irritated me, and I sometime had to book using expedia, when I wasn't in the mood to call EK/MasterCard. You still can choose seats while using Expedia on EK.com after the booking is paid for, but I prefer booking with EK because when booking with a travel agent, third party, any changes before the journey begins must be done with them, which is annoying at times.
Anyway, I was thrilled a few months ago when I went to book my flights, and saw that Amex was listed as a possible card, so it made my life much easier. Never using a travel agent for EK flights again!

The reason that MasterCard apparently didn't go through, is because they think that since my card has a US billing address, a booking in F/J originating internationally is fraud.

Anyway, stay on the phone with MasterCard while booking, as they will get a notice of the payment trying to be charged, and they can allow it to go through. Good luck!