, I’m sorry you are running into issues with your card being rejected by our payment system 
I certainly understand how frustrating it is to not be able to purchase a product you want to use and have used http://gifrific./wp-content/uploads/2012/09/Fry-Shut-Up-and-Take-My-Money-Futurama.gif myself a few times to voice my discontent about not being able to pay for something. I’m looking at you HBO / Game of Thrones.
I wish there was an easy solution to , and I would still suggest contacting @epicgames. for help as they might have more details on what went wrong payment wise, but my fear is that other than waiting for us to get better payment coverage, your only other good options are to use a different card or talk to your bank and inquire what went wrong.
Another reason I am suggesting contacting @epicgames. is that based on analytics I saw, they are able to help a large percentage of folks to pay for the engine, but I am not sure how many of those simply tried another card.
UPDATE: I forgot to mention that broadening our payment provider reach is a focus and there are folks dedicated to . My apologies to those affected by our sub-optimal coverage.