nether

I won nether chosen pack, I add the guy he gives me the code, I try the code it says it's duplicate. I say to him it's a duplicate, he says no, I try it again, and it is a duplicate, he asks in which country I live, and then he says it's probably because of my country (aluding it's region locked or what?) I ask him whether he was sure the code was real, then he said that he worked at that companym then he offered me some other games instead of nether, I said no and said to him to request a new winner. He has contributed before and has 100% of sent gifts. Has anything like this ever happened to you and have I done the right thing? Is Nether region locked? I'm from Serbia, which is not near Russia, and I have never had a region locked game problem before