What do I do if my wife wants a divorce and I don't?

I am a sunni muslim. I got married on October, 1995 and have a 26 years old unmarried working daughter. For the last one month my wife is living separately with her daughter. Yesterday I received a notice of Khulanama from her stating that she doesn't want to live with me and seeks divorce through Khula and also said that she doesn't need the Meher Or any other articles from me. The said letter was signed by two witness also. Now the query is that in this case divorce happened although I don't want to leave her.