Please check and see if you have logged in with the right account.
If you have logged in with the right account and you are still missing Diamonds or Stars, it might be because of a bad network connection.
Please check your network connection.
If it still does not work, please go to the 'My Page', select 'Help center' and submit a request with an image of your iTunes receipt of the purchase you've made and press send. The receipt should include Order ID (Starts with M), Total amount, and Date. Then, we can give you better feedback.
*To find your receipt: https://support.apple.com/HT204088