I have the trouble with listening?

Well, I am an Asian American. English is my first language. I have been US for 3 years already. I have no problem with speaking, reading and writing (expect some grammar issues). Whenever I make a phone call to a company for solving my problem (I call T-Mobile today), I don't always understand what are they saying unless they repeat the question again. I think I would understand it better if they write down the question (just saying) (I think they speak to fast, that's why I can't always get what they saying). I feel so depress because I can't even have a conversation with people in English. Does anyone have any idea of how to improve my listening, so I can talk with people fluently instead of constantly asking people "what" ? Thank you so much if you help me to improve my listening?