Write to dmitrii.raev@gmail.com. This is one person rather than a support desk, so a reply takes a few days — but it comes. Include your device model, your OS version and the game version (Settings, at the bottom of the screen).
Progress is stored only on your device and there is no server copy, so deleting the game deletes it for good. If the game is still installed, write in — sometimes the profile is intact and it is the backup that is being read.
Restart the game with the network on: an unfinished order is redelivered by the store on the next launch and the gems are credited then. If they are still missing, write in and include the receipt from Apple or Google.
Chests are bought with in-game coins only, never with money directly. A chest draws one species from a pool, and every species in that pool is equally likely. The size of the pool, and how many of its species you do not have yet, are printed on the chest in the shop, before you buy.
Settings, then "Anonymous usage data". It takes effect immediately, not at the next launch.
Settings, then "Ad privacy settings". That row appears where the consent form was shown — the EEA, the UK and Switzerland.
Settings, then "Reset progress". There is no undo.