Sorry, but this is utter BS. Blaming Microsoft for being "limited by technology and restrictions" is a pretty bad excuse for screwing over your valued customers, who have paid for the now worthless lifetime license. YOU chose to create a new product, not Microsoft. You could have easily kept the app on the UWP platform and update 5.x to 6.x without making your customers pay again. But no, YOU chose to create version 6.0 with a different underlying platform, so of course it's considered a new/different product. Regardless, you could have worked out something to let users upgrade for free, but again YOU chose this path deliberately in order to create a new stream of revenue. I'd be totally fine paying for an upgrade hadn't you advertised and sold the previous version with a "lifetime license". The current situation is simply NOT ACCEPTABLE and should be considered SCAM.