In order to fix the issue, try to turn your device off and then on. If it doesn't help, you need to contact your SIM card provider. If they can't solve the problem, open the device, tap Start and navigate to Settings > All Settings > System > Memory, select Factory Default from the Clear Storage tab, type 1234 and tap Yes. Alternatively, press at the same time Volume Down, Talk/Send and End/Power buttons and then the Volume Up one. After that, press Volume Down to restore the factory default configuration.