Relax, no need to get angry and come up with "misleading", "consumer protection laws", etc.
Just follow the instructions on the screen and it'll work.
It might not be the most obvious thing, but as @Andrew already stated, just enter your existing supporter license into the upgrade page and you'll receive your v4 upgrade license.
You also have the chance to spend some additional money if you want to support the development of a brilliant tool like Alfred even if you've bought a Mega Supporter license in the past. I happily did that, because Alfred is one of the greatest tools ever and I wouldn't miss it on any Mac I own.