If your purchased Twists aren’t immediately reflected in your account balance (upper right corner), please wait for five minutes and make sure that you’ve received a receipt from the Google Play Store (the iTunes Store sends out receipts at the end of the month). Normally, a missing receipt means that no purchase has been made.
In the unlikely case of you having received a receipt but no Twists via the “Report an error” button in the settings and make sure to include the order number and the date of the receipt.