deregister broken car but letter at the bank

Hello guys, my girlfriend has a car with a transmission damage that she doesn’t want to be repaired! The car was a gift from the mother who was financed (not yet paid off)! Since now no more reperture is worth my friend would like to unsubscribe the car, however you need the vehicle letter and the license plates for it…! The mother does not care about it and gives us no information and my friend would have to pay for 1.1 taxes + insurance for a car which since d em 08.11 is no longer driving…! We are looking for a way not to pay these amounts and get rid of the car as quickly as possible (which is no longer worth paying off the financing due to the transmission damage). For the cancellation we also do not have a private property to park the car somewhere. I am pleased about any help.