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When I’m already on a call, if someone else calls me at the same time, although I can hear the current caller he/she can’t hear me. The new caller is unable to leave a message either. Eventually both calls drop off.
I have checked caller waiting. I have spoken with customer services. They asked me to disable call waiting and then enable it. They also sent me a replacement SIM card. Nothing worked.
As a process of elimination try your sim card in another phone and then see what happens @Watchdog60
Sometimes if a sd card is failing this can cause issues so if your using one please remove it to see if that helps.
Make sure your phone's software is updated via Settings > Software Update in the phone.
Make sure your apps are updated via the Playstore and in your Samsung Galaxy Store.
Some generic troubleshooting tips are …
1, Put the phone in Safe Mode which disables your downloaded app's but let's your stock app's keep working. If the issues stop then this highlights a downloaded app as the possible issue. Come out of Safe Mode and start deleting your most recent downloaded app's one at a time until it stops. https://www.samsung.com/uk/support/mobile-devices/how-to-start-my-galaxy-device-in-safe-mode/
2, Clear your phone's System Cache Files by turning your phone Off and then from a set series of button presses go into the phone's System Files and clear the cache. No information is lost this way. You may need to insert your headphones or hook upto a computer with your data cable to get to this menu on the phone.
3, Factory reset after backing up and removing any relevant sd card.
Current Phone > Samsung Note 20 Ultra 5G - SM9860 Snapdragon.
Samsung One Ui 3.1 / Android 11.