Did you file a claim with their local BBB office? At least that gets you a call from someone higher up the ladder, someone that you might be able to talk into giving you a "customer satisfaction" refund in place of the actual rebate. Many people have had success in this, but you have to approach it properly. Stop trying to force them to issue the money for the rebate because for some reason giving it to you when you didn't qualify is not allowed but giving it to you for some other reason is just fine! Instead, start negotiating for an equitable settlement because of how poorly they handled this from the beginning (CSRs who told you to go for it, all of the rebates searchable on their own site, etc), how poorly you've been treated and how it took them so long to get to the point where they denied your claims.
Good luck and don't give up, you can get all of the money!