How to Talk English Like a Native Speaker?

According to American Culture my English level is C2. However I do not think the same way. I still am not able to talk fluently. I even can not construct a long sentence which requires a huge quantity of vocabulary. I was expecting better than that. When I watch movies/TV series without subtitles, I usually have no difficulty in understanding. When it comes to talking or writing, I am a disaster. What should I do in order to speak and write better? Any suggestions would be helpful. Thank you already for spending your time.