Default In need of some assistance:I9300GSMH

Hello, First post here on Xda, Nice to meet you all.
I'm looking for some serious help with my new samsung galaxy S3GSMH International version.

Long story short, My girlfriend lives in germany, While on holiday there I purchased a samsung galaxy s3i9300 and was told it will work in any region any network due to being factory unlocked.

In germany I was using a sim card from VIVA mobile or something of the like and it worked fine.
After I returned home, I switched in my UK Vodafone sim card, A message then popped up saying, Please select sim service:vodafone UK/Vodafone UK prepaid.

So I chose Vodafone UK and clicked on OK, I thought everything was fine untill i tried to make a call and got, Not registered on network.

Now I have searched for days in all types of threads to get this fixed, I have tried flashing stock firmware with odin/emergency recovery Via Kies/Flashing modems/flashing patched modems/patched kernals/Ariza patch/Ariza patch Jb.

My Imei is fine and matches under the battery, The S/N also matches under the battery.

So I just don't understand it, If it asked me to choose which sim service surely that means it has some type of connection with the network? I have full signal bars too.

Is there anything else i need to do to get this working? Because I am at a loss, And I obviously can't take it back due to the shop being in germany

Any help or input is extremely appreciated!