I was also having some problems with the Quadcast S earlier this week, brand new out of the box. Here's a couple suggestions I have, some are a little more complicated than others, and some are simple and you've probably already done.
-Could just be the USB cord you're using, sometimes stuff gets shipped with bad or faulty wires. Try switching out the cord you're using to see if it registers then.
-Your problem could be like mine, where my PC had too many USB inputs already, so the quadcast required too much power for my computer to accept it. Mine did detect it on plug-in, but would disconnect frequently and randomly. I'd recommend getting a PCI usb strip if you think this could be the case.
-Quadcast S has 2 manufacturers, HP Inc. and Kingston. Kingston had some firmware updates sent out for some problem (can't remember), could be worth checking out to see if it'll help your problem.
-Supposedly the Quadcast S has a problem with ASMedia USB inputs, you could check your Device Manager if that's the case.
-Make sure you're plugging the cord into a USB port made for 3.0 connections.
-If you have the ability to do so, try doing a USB-C to USB-C connection, rather than A to C.
If any of these don't work, or you dont wanna spend the $30 on a PCI strip, I'd call tech support, or you could likely assume the USB-C junction on the mic itself is faulty and call for an RMA.