Online car reservation--the lady is saying they don't have cars...?

I need a car asap, and yesterday night i reserved a car through the website--today a lady from the rental office called me and told me that they did not have enough cars--what should I do? call the company and tell them like I have important things to do; therefore, they should find a car for me? or what? thank you I wanna get the same car at the same rate.