Being evicted i need to know my legal rights and what i can do.?

A little background info about the problem.Me and my 2 other roomates were living at our apartment for a little less than a year. My other roomate who had his name on the lease took it off so for us to stay there we had to add our names to the lease. The management company im dealing with is very disorganized and they are claiming they did not receive one of the forms needed for the application. We paid this months rent and they are saying that we have to move out by the 18th. When i called the management company they were not helpful at all even when i told them we gave them everything. What can i do to fight this eviction what are my legal rights? any help would greatly be appreciated.
I currently live in California. The only person on the lease was my other roommate who moved out but they told us that we could add our names and we gave them all the proper forms and now they are claiming we have to move out.