Knetbooks Sent an USED code and won't provide a refund Internet

I simply ordered 2 ecodes for digital books and they were both "invalid and in use." I contacted Knetbooks, chatted with several customer service representatives for a refund and I was told "
I do apologize but where the item is considered used we are unable to refund you for the item where its not guaranteed with an used item it states on the website "Not guaranteed to come with supplemental materials (access cards, study guides, lab manuals, CDs, etc.) " - All I bought was supplemental materials. What company accepts returns for INVALID and USED access cards??? And then, ships it right back out????? SO, I spent $28 on two pieces of cardboard, on some arts and crafts. If I wanted some cardboard, I could have checked in my neighbor's garbage can. So, I lost $28, had to cram 2 weeks of assignments in 3 days, spent $129+ on my school's website for UNUSED codes, and I got some really cool cardboard (: