Sixt Blocks My Account and Fails to Refund My Canceled Car Reservation

I booked a car through Sixt app and paid 5 days before my trip. On the day of the rental, when I arrived at the office to pick up the car, I was told that my account had been blocked and I needed to contact customer support. I had received no prior notification about this — nothing at all. First, Sixt support wrote in one email that my reservation had been canceled and that I would get a refund within 72 hours. Then, in another automated email, it said the refund would take 5–7 business days. It has now been more than two weeks, and I still have not received my money. Sixt support keeps insisting that the money was refunded, but my bank confirms that no refund has been processed. This back-and-forth is unacceptable. Terrible service. Never deal with Sixt! Reservation number: 9725155416