Thank you both for responding. I did have a misunderstanding but I have cleared it up with billing at SL. I was having a problem on marketplace and when I saw the message on the process credit page I thought it applied to me and it was causing my problem.
Turns out there was a glitch in the system with my account trying to use marketplace which has been solved. My account is fine, I can continue using my bank card for purchasing lindens and paying fees. AND, I now understand the process credit should I ever need it.
My thanks to everyone who helped me including SL who were so quick to fix the actual problem.