Called customer service and the guy just wouldn't respond, called again, got hung up on

I got a notice about a refund from a customer that says they never received the item. I sent the package and tracking shows they got it. Amazon issued the refund, no questions asked and now I can't even put in a claim since it isn't a return. And when I try and get a review, it says it is outside the window which it is not. So frustrating. A brand-new way for customers to totally screw over sellers and Amazon has no problem with it. Would love a Mod to respond and tell me how I am supposed to dispute this? I finally did chat with a support person but they weren't helpful. They told me I had to talk to customer service since they initiated the refund. Of course, they told me to talk to seller support. That was useless. I am so tired of getting the run around and customers getting full refunds and shipping costs returned even when it is a buyer issue like "bought by mistake". My safe-t claims lately are being denied or I am given $4.29 of the $21 in shipping charges that I asked for. Ridiculous way to do business.