Also; there are some other steps that you should look into.
Find your sim status in the phones settings. Look over to make sure they show the Sim has registered on the public mobile network. That the status is active. Etc. if not;
1) power off your phone, wait a minute. Restart and check if the sim has registered and connected to the network.
2) if that fails. Again power off the phone, remove the sim card from the device for a minute. Also inspect it for damage, use a dry microfiber cloth to clean off any skin oils or debre that may effect it's communication with the phone. If you have another device, try inserting it into that phone to see if the service picks up on that other phone. Then, once all that is done, reincert the sim into the phone you want to use.
If the sim worked in the second device, but still does not connect in the new one... It could be the phone that's the problem.
If the sim didn't work in the second device either, and continues to fail to connect to public mobile services, you may have a defective sim.
