Apologies for the confusion. I have checked with my bf and no, the phone was not "jailbroken" or "unlocked"- I am an iphone dummy. I will take it to a store here in UK and see what they say. Apologies for headache.
There is nothing you can do. As I pointed out already, you can't buy an unlocked phone where you said you got it and the carriers there don't offer unlocking. Somebody is lying. It's not possible for that phone to be unlocked.