Dual Citizenship (Father had Taiwanese citizenship when I was born)

Hello, I was born in the United States, my mother being American, my father being Taiwanese. My father still had Taiwanese citizenship when I was born (he also has a US greencard, not sure if that matters) and then a few years later gained his American citizenship and no longer has Taiwanese citizenship. Now I am 20, and I was wondering if I can apply for dual citizenship for Taiwan since from what I have read, it states that it depends on parents citizenship at time of my birth. If I am able to apply for dual citizenship, what papers must I have to bring and give to attain my dual citizenship? Also, where/ who woud I talk to? Also, if i have to serve in the Taiwanese military for a year, am I allowed to serve after I have finished college in the United States? Any information/help would be greatly appreciated.

Calling Satellite TV (the best guy to answer your questions probably )