This macOS version is not supported

I'm on macOS High Sierra 10.13.6.
My Paralells desktop windows pvm had completely stopped working on my computer. If I opened it, my whole computer would simply lock up. I would have to hold down the power button and reboot. I've tried updating my OS. Nothing. So I thought maybe if I upgrade Parallels, it will work.

I was running Parallels 16 before - There are banners to upgrade to 18 all over the software (so many ads in paid software, crazy), so I clicked through and bought a permanent license for it. I'm trying to install it, but now it's telling me that I can't actually use this software on my computer after all. Would have been nice to know that before dropping £100 on it. Also not really appropriate to advertise it so heavily to someone that can't use it. Whatever.

But here's the kicker. Now that I've run the installer for 18, it's also deleted my license for 16, but it won't accept my new license because it's the wrong version. So it's basically rendered my whole install parallels unusable.

Not happy. This is highly unprofessional. Please advise.

 

It now wants a Parallels 17 license key. I don't have one and it won't accept an 18 key. It also won't allow me to install 18

 

Hello John, please be informed that in order to activate Parallels Desktop for Mac Upgrade license you must have a Parallels Desktop legacy permanent license to act like the previous version key while activation. If confirmed we will be able to initiate the refund for either Parallels Desktop for Mac Upgrade license, so that you can purchase Parallels Desktop for Mac full version. Thanks.