Here providing MIUI 8 Ringtone Problem and Solution.
Issue : After upgrading the software to MIUI 8 unable to change the custom ringtone. It sets to the default ringtone. After changing the ringtone it shows the new ringtone but when someone call then it rings the default ringtone.
Solution : This is the issue with single SIM card in the phone. If you want to set the custom Ringtone. Please follow the below steps.
1. Insert two SIM card in the phone (You can use one temporary SIM card).
2. Go to Setting Menu
3. Open sound and Vibration option
4. Click on Phone ringtone option
5. Disable the Single Sim Option
6. Now set the Phone Ringtone
7. Check by calling on your phone
8. Now you can remove the temparary Sim
9. Now you are able to set custom ringtone
MIUI 8 Custom Ringtone Problem Solved Video here :
Above video is related to Redmi Note 3 MIUI 8 issue. Redmi Note 3 Custom ringtone issue.