Buying Runescape Membership with a Playspan Bought Ultimate Game Card?

I bought an ultimate game card online with playspan. I was going to use it for a runescape membership but I don't know how. It says go to this, click that, blah blah blah. I followed those instructions, but I can only get as far as the page where it asks for the code on the back of the ultimate game card. I didn't by a physical game card, I bought an online one. I can't find it, Is there a special place I have to look in the email that was sent to me, or a special part of the website. Because I bought an ultimate game card that I can't use and its agitating me more every minute. GOD! Why can't runescape just use normal payment transactions like paypal!?