Booking cancelation refund

I booked and made payment online for a car with Avis ,I was told a certain amount to have on my card to make payment and collect the car ,when I got there I was requested to make more than ×5 of the price I was asked to pay ,it's even on the email I was sent,now I want to cancel the booking, not because I wanted but because od the misleading information I was given.i need my refund, they refusing to cancel and refund me.....worse experience ever