I've had the same happen to Wifi plugs bought as recently as three years ago. They all seem to use different (buggy) apps and route the signal to the plug through some obscure website (usually in China). Of course these sites and domains will go down from time to time. Plus, they all use different, undocumented protocols so homebrewing a new controller app is a no-no.

Lesson learned, I now carefully research any smart home stuff I buy now to make sure it has an accessible API I can use if the cloud stuff goes down.