Because the UI is so bad (each time I searched, it changed the month), I ended up booking March instead of February (my dates in February corresponded to the same days in March). The Sixt agent told me he didn’t have the car I ordered so he couldn’t change the booking (I have photo evidence of the car being on the Sixt lot), but instead he hired me a small car for one night to get the the hotel and then I came back and picked up a different car that he arranged from another company and had to pay cash. I have contacted Kayak with evidence that the booking was cancellable, but I haven’t been able to contact Sixt through the number on the booking, nor e-mail, nor the website to cancel or even change the booking. Kayak are taking an age to do anything, so I’m reporting the booking charge on my credit card as fraud.