You can try
AT+CMGF=1
AT+CMGL="all"
This can read all the message
AT+CMGF=1
AT+CMGL="rec unread"
This will read unread message
You can try
AT+CMGF=1
AT+CMGL="all"
This can read all the message
AT+CMGF=1
AT+CMGL="rec unread"
This will read unread message