Unable to set a default SIM card for calls

If you're unable to set a default SIM card for calls, here are a few steps you can try to resolve the issue:
1. Please go to Settings APP on your phone to check that the correct SIM card is selected for calls. If you can’t see the option to select a default SIM for calls, check whether both SIM cards are active and properly inserted;
2. Clear cache for the Phone APP;
3. Sometimes a simple restart can resolve any software glitches preventing you from setting a default SIM;
4. Please check if there are any updates available on your phone. Updating the software can fix bugs related to dual SIM functionality;
5. Reset network settings on your phone.
If none of these steps work, it could be a bug with the phone’s software. In that case, please submit feedback through your phone for further assistance.