You need to talk to them and convince them that you are only interested in playing the game you love. Explain to them why it is important to play that particular game and what it will mean to you if they allowed you to play the game that you love.
This same thing happened to me just a couple days ago. what i did was i told them that the sport that they were thinking of was not so interesting to me. then i said i like this one better. then showed them a video on youtube about it