You may have received an email from ‘Amazon’ informing you of a reward for your custom.
Basically this is a scam and not from Amazon at all.
I am fairly vigilant when it comes to emails like this however in my case I had recently ordered a few things from Amazon but my Amazon account is UK based and the rewards email was for a reward in dollars. So that made me suspicious even more.
One way you can confirm this is a scam is to hold the mouse over the highlighted Amazon links and you will see the real link address you would be taken to if you clicked them, clearly not Amazon at all.
Amazon themselves are aware and have warned of this scam, details here: https://www.amazon.com/gp/help/customer/display.html?nodeId=15362281