a) If this issue only occurs in certain places, move to a location with a strong signal and try again.
b) 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.
c) Check whether “Blocked numbers” or “Filter spam calls” is active on your device: touch “Phone” app-> touch the settings icon at the top right corner->“Settings”->check “Blocked numbers”.
d) Please try to restore functionality by turning Airplane mode on and off or rebooting the device;
e) Please contact your service provider to check whether any response from you is needed for your service account.
f) Try to reset or update your device. (Refer to “How can I perform a factory reset on my device in the Back Up & Reset module” & “How can I upgrade my device in the Basic Settings module”).
If the previously described options do not help, you can contact our hotline or repair center to get more professional technical assistance. Find the hotline or repair center information from the official website or APP “Support Center”.

Note: This Q&A question does not apply to the Wi-Fi version of the tablet.
Available settings and menus may vary depending on device model and software version.