repeted problems ordering with nativdsd.com

Over the years, I have ordered from nativedsd.com. Often, approval for my charge card "fails authentication," but after repeated tries over a few days, it generally finally works, and the order is completed. But sometimes I give up. There is nothing wrong with my charge card, and my charge card issuing company has confirmed this, and they have no record of a requested approval in instances where the authentication failed. I have occasionally complained to nativedsd.com, but they have not been willing to investigate on their end. However, I have been attempting to make a purchase for several days without success, and this latest instance has resulted in more repeated failed attempts then I ever remember. Has anyone else had this problem, and if so, what did you do to resolve it?