Sim card block on my samsungSGH-F250 phone

Question

Recently i bought my samsung SGH-F250 phone from a Digicel shop in Fiji. I later found out that i am unable to use my vodafone sim card in that phone and that Digicel has blocked it. How do I unblock this?when i put in the vodaphone sim it asked for a password but i have no idea what it is.