Do you have a Game Center active in phone settings?
The only way to make sure your progress is saved regardless deleting the app or changing device, is to save your character in Game Center BEFORE deleting the app/changing.
To do so, go to More -> Settings in the old device and assign hero to GameCenter

If you see green text "already assigned" - it's done.
After that log on the same GameCenter account on the new device and launch Questland. You will be asked to load your old Hero from GameCenter - you will see hero's nick and level. Very important: make sure to pick the same server while signing in! (if you have been playing Questland for long, it may be the VETERANS server)