AFAIK, HughesNet does not have a "$50 VISA Gift Card" offer. Some independent HughesNet Retailers may offer this but it's not sponsored by HughesNet.
There is a $50 discount offered in some areas. Until June 30, it was offered as an instant $50 discount off the first month of service. On July 01, it became a $50 rebate after the first 90 days of service, again offered only in some areas.
How, when and where did you order your HughesNet service?