Default "Not registered on network" issue after updating my Android to 4.3 on Galaxy S3

Hi guys, after whole day of searching and testing I couldn't find any solution to fix my problem. That's why I am here to ask you for advice.
I have Samsung Galaxy S3 and I have recently updated Android version via Odin 3.09. I have used that website to get android system software (or whatever it's called):
samsung-updates.com/device/?id=GT-I9300
with version 4.3 dated on 16.01.2014 for region 3IE (Three, Ireland)
After that I have noticed "Not registered on network" message when I tried to call someone. I have also noticed that my IMEI number has been changed to:
35371xxxxxxxxxx (x is new numbers comparing with imei number under battery)
I hope I have provided enough info about my problem.
Is there any idea to fix this?