Incoming Call Issues – Unknown Caller, Delay, or No Ringtone on OPPO Phones
🔍 Problem Description
Incoming calls display as an Unknown number. There is a delay before the incoming call is shown. Incoming calls arrive without a ringtone even when not muted.
⚠️ Cause Analysis
1. Incoming Call Display Shows “Unknown”
The Caller ID service has not been activated by your operator.
Calls from certain special numbers may appear as unknown (normal behavior).
SIM car is damaged or not working properly.
2. Incoming Call Delay
VoLTE network issues or local operator network instability.
Poor or interrupted signal in special areas such as:
Bus stations, classrooms, stadiums
Basements, underground garages, elevators
High-rise buildings or areas with fast movement (cars, trains, high-speed rail)
System software issues or an outdated software version.
3. No Ringtone on Incoming Calls
The speaker is blocked by dust, or the speaker's hardware is faulty.
Mute / Do Not Disturb mode is enabled.
A third-party app in the background is occupying the audio channel.
The phone system is outdated and is causing ringtone compatibility issues.
🛠️ Solutions
✅ For Calls Displayed as “Unknown”
Check whether the Caller ID service is activated with your operator. If not, please activate it.
Remember, some special or private numbers will appear as “Unknown” — this is normal.
If the SIM card is damaged and is causing abnormal number identification, replace the SIM card.
✅ For Incoming Call Delays
If calls are not working properly on the VoLTE network, try disabling VoLTE (note: on some 4G/5G telecom cards, VoLTE cannot be disabled).
If the same operator/network also shows delays on other phones → this is likely a network provider issue → contact your operator’s customer service.
If only OPPO phones are affected → collect details using the “signal network type abnormality” template and submit via quality feedback.
If you are in a special area with an unstable network, move to a location with better signal.
Update your device to the latest system version to ensure network compatibility.
✅ For No Ringtone on Incoming Calls
If the speaker is blocked by dust or a hardware fault, the phone may need cleaning or repair. Visit an authorized OPPO service center.
Check if the phone is set to Mute or Do Not Disturb mode. Disable these settings.
Some third-party apps may occupy the loudspeaker channel. Clear all background apps or restart the device.
Ensure your phone is updated to the latest system version to avoid compatibility issues.
📌 Final Note
Incoming call issues can often be linked to network quality, SIM card, or phone settings. By following the above steps, most problems can be resolved.
If the issue persists after troubleshooting, please take your device to the nearest OPPO authorized service center along with your purchase invoice and warranty card for further diagnosis.