help to unlock GT I19300

I need help to unlock my mobile.
its on 4.1.1
baseband I9300XXDLIB
kernal
3.0.31-204919
se.infra@sep-67 #1
SMP PREEMPT fri sept 21 21.52:00 KST 2012
build number
JRO0030.I9300XXDLIB

to explain 1st, the mobile was on THREE network and now locked, I have tried myself by using ODIN and downgrading from the original firmware 4.1.2 to and earlier version 4.1.1 which I have read is needed.

This is how far I have got,

#197328640#

Main Menu
[1] UMTS (this option is not displayed)
[1] Debug Screen (option displayed and selected)
[8] Phone Control ( option displayed and selected)
[6] Network Lock (option displayed and selected)
Options [3]Perso SHA256 OFF (this part of the process is not displayed on my phone screen,

the options that are on the screen are
menu not exist
press back key
current comand is 186

sorry if this is the wrong forum but I could not find anywhere else to post this

and I dont want to keep going on and trying things i dont understand,

foriegn sim inserted but not geting a prompt to unlock

es0tericcha0s said:

This has absolutely nothing to do with what the OP is looking for.

OP - It's not going to work for you anyway, unless you have an EFS backup from when you were on 4.1.1. Once you update to 4.1.2, the EFS partition changes and does not allow the free methods to unlock the phones. Downgrading alone will not solve this, which is why you need the older backup. Without this, you will just need to purchase a code from a respected vendor.

Read here for more info: http://xdaforums.com/galaxy-s3/help/carrier-unlock-gt-i9300-android-4-1-2-t2454188

Click to expand...

Click to collapse

thanks for the info, its still a hrd subject to get my head around, Ive got a vendor code but when i put in a new sim Im not getting prompt to enter the code

phone info

es0tericcha0s said:

Do the baseband and IMEI still display in the About Phone section in Settings? What message do you get when you input the foreign SIM card?

Click to expand...

Click to collapse

Both of those are still showing, but there is nothing displayed when I put in a different sim card