Sixt review: very high fine for being late for one hour

Good morning,
I have rented a car for four days: 27/9-1/10 via rental cars.com .I have been late for one hour ang charged for 216.35 euro. A bill is attached. They say that they charged another tarrif for the previous days also because it is a pre-paid voucher. I tried to send them a mail and it did not help.
Would you please help?
Thank you very much
Best regards

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