I doubt that when he ended with "Hyung," he was telling you to call him Hyung as his name. His actual name is Hyungwon. If you were male, you wouldn't call him Hyung Hyung because his name is not Hyung. You would call him Hyungwon Hyung, or just Hyung. He would know which is which by the same reason. If he wanted you to call him by his name, he would have used "Hyungwon" instead. Rather, I think he was trying to be more friendly by using "hyung." (FYI: In Korea, it is possible for a female to call an older male friend "hyung," meaning brother. Though it isn't used too often, some people who don't want to call their friend "oppa" may use "hyung" as a more comfortable way of addressing someone in their friendzone.) But as you said, if he changed his name to "Hyungwon Oppa," it's a bit different. I agree that he was implying that you should call him Oppa. Maybe he wants to be called that. So you may call him "Hyung," "Hyungwon Oppa," or "Oppa." All three are correct, it just depends on how you would like to call him. The choice is up to you. Hope this helps! :)

The problem is that you can speak Korean language. In American style, you can call him "Hi Hyung" or "Hi Hyungwon". Many Koreans use the first syllable of the name as the English name because English native speakers have difficulty in pronunciation of the full name. I knew a man whose name is "Kim Hwancheol"(김환철) and English name is "Hwan Kim" If you want to add the title 형 or 오빠 and the name is ended with consonant, it is common custom to add suffix 이 after the name for easy pronunciation. For example, 형 오빠 => 형이 오빠 형 형 => 형이 형 형원 오빠 => 형원이 오빠 형원 형 => 형원이 형

His name is HyungWon. In Korean peaple don't say the first sylable Hyung. So You can say HyungWon or HyungWon Oppa. HyungWon Ssi(형원씨). Oppa Many Guys wants to that word. It is your choice.