Sixt Charged Extra for Car Rental at Bru Airport, Requesting Refund

I rented a car from Sixt at Bru Airport with a total cost of 425 Euros. They charged 725 Euros to my card, including a 300 Euro provision. I was told that returning the car to a different airport in the same city would be fine with an additional 25 Euro fee. However, after a smooth return, I was charged 478 Euros instead of the expected 450 Euros, and this charge was made separately from the provision. Now, my card shows a 725 Euro provision and an additional 478 Euro charge.

I request a refund for the overcharged amount.
Why was an additional charge made without my consent? Shouldn't it have been processed through the existing provision?
The separate charge was corrected, but I'm not sure if it was a coincidence or a response to my inquiry. Regardless, I appreciate the correction, but the issue of the excess charge remains. Please address this matter promptly.