Well, I emailed SilverCar support and got an answer today. So apparently, I actually got my $25 rebate, but didn't know it. I got a random email back a couple of weeks ago saying I had a claim code and to click here to redeem it. It had not indication on what it was. As it turns out, that was the rebate and I had marked it as SPAM!

Keep your eyes out for an email from [email protected] This is not junk. I expressed my frustration with this to their support as it totally looks like phishing. I did get the option to have a physical card mailed to me or get a virtual card to use online, which seems to be working :-)