What should I do if I didn't get my rewards after inviting my friends?

Three conditions need to be satisfied in order to get the 20 credits REWARD:                                              
1. There're several entrances to send invitations, the valid reward place is More->Credits >Earn 20 credits.  
2. Your friend's device has never installed Dingtone or Dingtone (a sister application of our company).  
3. Your friend need to finish the process of clicking the link in the invitation message, downloading the application and registering as a Dingtone user.