Have you contacted Corel about your issue? I'd be surprised if they can't help you re-enable Painter 2019 if it's a legit purchase and the trial has caused it to deactivate.
Just incase anyone else in interested in the app, the Painter 2019 Humble Bundle has been reactivated (has 3 days left) which would mean you can snap it up for $25. I've had a tinker and it seems pretty powerful (loads of options) but I feel it lacks the immediacy and intuitiveness of ArtRage. Maybe an app to grow into?