[Q] Galaxy S3 to stock - No cell conenction

I have been using custom roms for 2 years. Decided to go stock. I am in Australia, and my Galaxy S3 (T) is bought through a group called Crazy Johns, but they are owned by Vodafone.

I found a stock ROM:

I9300XXEMC2_I9300OXAEMC2_BTU

I flashed it successfully, and all starts up nicely. However, I can't get any cellular data. No calls... no data.

I manually try to connect to Vodafone network in the Network settings, but then get told "Vodafone unavailable".

I then tried to download a new modem, hoping that was the issue.

I got one called modem_RIL_CWM_I9300TDUEMB1

No luck.
I then thought, OK, maybe Vodafone isn't allowing my pone on the network, because the firmware isn't a Vodafone official one? But, that can't be right. I could have bought my phone from outside Australia.

Funny thing is, when I got the phone, it shows 'Crazy Johns' on the settings screen. Now, I have no mention of Crazy Johns. Is it modem related?