Perso Lock (Sim) Help Please

Hi All,

I'm at a loss, would be tremendously grateful if anyone could help me save my galaxy:

- My phone is an 850F, purchased sim-free from Carphone Warehouse in the UK. It is rooted.

- Recently I inserted a new sim card. The phone worked perfectly well for a week.
- Upon rebooting yesterday, the phone awoke to a message stating the sim was locked and prompted me to enter a code.
- The phone could no longer utilise the network.

To troubleshoot:
a. I inserted the sim in another phone - the sim worked fine in this other phone.
b. I tried 2 other sims for different countries in my 850F (O2 UK, T-Mobile US) - both of these sims seemed to work fine.

c. I contacted the network of the new sim, they suggested I try 2 different 4 digit unlock codes - both failed.

d. I received a new sim from the same network - using it presents the same error message and prompt to unlock the sim.

e. Finally I wiped the phone, re-rooted and installed a new rom (Cyanogen 12).
- This has not solved the problem. In Cyanogen I receive the message: "Phone is Perso Locked". Again I am prompted to enter a code.

Thanks for reading, any help or suggestions would be immense!

Cheers,

Tal