No receipt was received when picking up the car - only the car keys.
I had to base my knowledge about the fuel type only based on what I was told by Sixt, I didn't have a reason to doubt it.
The car was indeed MPV and the replacement car that we got was also MPV but then Diesel, so the MPV only Benzin theory doesn't really work.
Besides that, how could I notice anything strange during the week that I drove it until fueling it ? It came fully fueled by Sixt and the problem happened immediately after the first time that I fueled it.
Regarding the taxi, if Sixt cannot commit to paying the taxi cost without knowing first whose blame is it, they shouldn't promise it.

The story is quite simple : I just fueled what I was told, I didn't have a reason to doubt this information, nor a warning on the fuel flap or anywhere else to do something else, and now I'm requested to pay for their mistake.
I think that it is unacceptable. Dudi