iphone 4 abroad use only ?

i have an iphone 4 for sale which i purchased off gumtree 2 weeks back, unfortunately the person who sold it to me must have done an insurance job and got a new one which leaves me stuck with an iphone which only works abroad now i bought 2 weeks ago and it was working on o2 but the scum guy decided to block it through insurance, so im asking for 200 only as i am making a loss on this phone, i just want some of the money back, i cant take any offers as its already a loss to me, its in perfect condition still and u get the original charger and headphoens with it if itnerested please call or txt on 07733700879