I would contact the Politie in the region they say the accident happened . If someone left the scene the Politie would be involved . InwouI request the Politie Report From the law firm. This would be required for your auto or travel insurance

But if Politie is not involved then it is a scam and would contact Sixt direct via corporate channels. This sounds very weird .I live in the Netherlands. Even if you get a ticket via camera they send you the ticket from the Politie or police with photos and dates .

Rob