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Be careful not to try too many times or you'll hardlock the phone resulting in it needing to be sent away to be reset.
With some Samsung Galaxy phones you may need the mastercode also known as an unfreeze code as well as the Nuc.
Also the alternative network sim card needs to be activated i.e connects to mobile data etc.
And you need to be in the UK.
Current Phone > Samsung Note 20 Ultra 5G - SM9860 Snapdragon.
Samsung One Ui 3.1 / Android 11.
This is not unusual. You need to contact the NUC team for an MCK code but be prepared to wait sometimes up to 40+ working days !! They may accuse you of entering it incorrectly 3 times but this is rubbish as some work and some don't 😞