If your SIM is not working, the below trouble shooting steps may help.
Most issues can be resolved by powering your phone completely off, leaving it 15 seconds and then powering it back on again.
In some instances, you may need to manually connect your SIM to a network. To do this follow this process HERE.
It is a good idea to check your SIM balance to ensure you have sufficient credit. Log in to your account to check your balance and top up HERE.