I'm not sure I'm understanding the Sixt site.

My reservation is 2 weeks away. I have put the wrong pick up and drop off times for my car (basically they are opposite of what I need them to be - pick up at 9am drop off at noon) but when I attempt to swap the times, it appears as though I'll be charged in full again.

Anyone have experience with this? I'm not really trusting the system... There is no customer service to ask, the customer service is automated and only refers me to the website that seems to want to charge for the rental again... another $600 or so. I'm really trying to dump avis and this is my first rental with another agency... Any help is appreciated.