2) Check whether there are smudges or scratches on your SIM card's metal surface as a defective SIM card may affect signal stability. If necessary, contact your operator to obtain a replacement SIM.
3) Check whether 「Blocked numbers」 or 「Filter spam calls」 is active on your phone: touch 「Phone」 app-> touch settings icon
![](http://tct-open-document.s3.ap-northeast-1.amazonaws.com/image/Smartphones/南宫ng·28+20L/image3.png)
4) Please try to recovery with turn on and off Airplane mode or reboot the device;
5) Please contact your service provider to check if any re-activate process needed for your service account.