Phone is not connected to a network

The light indicates that the phone is not connected to a network. I have tried three different SIM cards in the phone and get the same result every time. Any suggestions?

Most important is that the SIM card is a 2G SIM card and that a 2G network is available at the location where you would like to use the phone. If you are uncertain about the latter, please contact your network provider. You may also test the SIM card with a standard mobile phone. When this phone connects to the network please check if that display shows it is a 2G network connection indeed. If it is and you can place and receive calls, the OPIS 60s mobile is likely to be defective. In that case please contact our customer support at contact@opis-tech.com. Please make sure to provide your invoice or order number so we can find the purchase in our system.
Best,
Frank