BP Gas Station

I got gas at this station at approx 1030am 1/*/19. I used a Target Mastercard $100 Value with $47.56 left on the card. At the self serve I charged $7.56 on gas leaving me with a $40 balance. SURPRISE I 5 minutes later found myself embarrassed at a drive thru Burger King as my card was declined. This gas station has put a hold on my entire balance of my card HOW IS THIS LEGAL? Basically stold my money - DISGUSTED - who is protecting the consumer here. How do they have the right to put any hold on a gift card , debot or credit card. This should be illegal. I now have to wait up to 72hrs to see if my balance is updated. UNACCEPTABLE I called the gas station and they wouldnt do anything