Getting tax refunded when using edge credit on gamestop.com

I just called the gamestop customer service number in order to get around $13 in tax refunded from a number of purchases over the last year that I paid for with edge credit, but was still charged tax on. I've heard about a lot of people contacting customer service and getting the tax refunded, but the guy gave me some bs about not being able to verify if the funds were tax-free. Anyone have any suggestions?