Unable to register on the NB-IOT network

I am using the following procedure to connect to a cell in a NB-IOT network for the first time:
I am using a Sodaq NB-IoT Shield deluxe, uBlox Sara N280 (NB-IOT module)
Then I Checked the SIM Card status: AT+CPIN? returns “ERROR”
So I tried to see if the SIM Card is registered: AT+CEREG?
It returns 0,2 (2: not registered, but currently trying to attach or searching an operator to register to)

I am sure of the APN name and the operator id (I tested the sim card on a mobile phone) so what I am missing?

Thanks in advance