Bad experience

I rented an economy car for 7 days from Nebraska to Texas. The first amount they offered me through email is $374. When I got there they charged me for $600, they said there should be something wrong with the system.

And after I return the car, they also charged me $340 without any notifications. I remember the maximum of the deposit was $200 right??? I also cleaned the car before I return it. I don't know why Avis can just charge my credit card without my permission..