1) Check that usage of the SIM has not exceeded the usage limit set by the Telco. This is usually limited to 10,000 SMS per month for Singapore Telcos
2) If Telco usage limit is not the cause, try to hard reboot the modem by unplugging it and plugging it back. Then reboot the CG-ONE appliance.
If issue is still not resolve, please contact us for a replacement unit for the modem