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1. Go into Clash of Clans and buy some gems.
2. Email Apple and say you never got the gems, since they do not have access to the Supercell servers they would have to refund you. Say that you've tried contacting them first but they never responded.
3. You are refunded, and your gems are still there.
Don't overuse, buying a larger amount is better than a smaller amount. after doing this about 3 times they will stop refunding you and ask you to contact supercell instead, so buy a larger amount of gems.