cant unlock iphone 4

dycey1888

after a 2 yr contract with vodafone they unlocked my iphone 4 so i transferred my number to another network,after developing a software fault my insurance company replaced my iphone but it was locked to vodafone network,when i foned to get it unlocked i was told as my vodafone sim is inactive they cannot help.i have jailbroke before but this fone is on ios 6 any suggestions how to unlock imei????????