If you request a refund for a specific pack you have purchased, the app store will return you the money and the currencies acquired will be removed from your account.

For example, if you purchased an offer that came with Ammo and Patterns and refunded the purchase, the game will not remove the items but revert these purchases into Diamonds. These Diamonds will have a real currency value, and the game will remove the Diamond equivalent from your Diamond balance.

However, if you have already used the purchased items and if you don't have enough coins/diamonds to keep a positive balance, that will not prevent the purchase to be reversed, and therefore, you will end up with a negative currency balance.

Then, you will receive a message stating that you must acquire a new pack in order to play, since it is not possible to keep playing with debt in your account. Keep in mind that we are not responsible for providing refunds for purchases, so if you have negative currencies and you haven't requested a refund, please contact Apple or Google support (depending on the platform you use).