[Resolved] iPhone Can't Make International Calls?

I bought an iphone from an ebay seller selling unlocked iphones for cheap. The phone is unable to make international calls for some reason. Have I been duped? Should I ask for a refund? Thanks.

Edit: Thanks for all the replies. First one was the case. Feel like idiot. 1 quick google search and realised had to use + sign at the start of number. +011 instead of 0011 like on android.